Why can't I build farm?

You need to research farming on the green Planetary Improvements technology branch before you can begin building farms.  The orange Xeno Engineering technology must be researched before Planetary Improvements (and other technology branches) will become available, though.  That should be one of the first things you research, in fact.

From your other comments, you are badly in need of the GalCiv wiki web site.  It should answer most of your questions and is an essential reference for beginners in particular:  https://www.galciv.wikia.com/wiki/Galactic_Civilizations_Wiki.

Not a bug. Farm buildings require Xeno Farming. Technically your initial colony *has* basic farms, which is what allows you to grow your population to 8 billion in the first place. In general, you don't want to put Farms on Farm Bonus tiles unless there's at least one Approval tile there as well, because growing your population also drastically reduces your approval rating, and as you upgrade the farms, they will soon provide far more population than you can please, since the more people you have, the less effect Approval buildings have. You definitely, definitely do not want to put a farm on your homeworld, since it already has a double pop cap. As a rule, one farm per planet. You want to keep your approval rating high because it increases birthrates, which means more taxpayers, sooner. If it's at 100%, you get double birthrates. This does not have to be universal approval--just 100% on a planet will increase that planet's birthrates, and if you are a Super Breeder, you get eight times normal birthrates.

Don't improve those first few colonies until you can afford it. Buildings cost a lot of money, and you can't turn them off with a slider. If you build any early improvements on your planets, make them Econ buildings.

One thing I always do that always seems to work is research Trade right away. Research trade, then sell it to everyone you meet. They will send Freighters to your worlds, which gives both of you a lot of bc per turn, and of course, you can send your own freighters wherever you want, the farther the better. Trade is, in many ways, better than taxation, especially if you get the U.P. vote to remove restrictions, which doubles Trade income. At one point, I had Master Trade, the U.P. voted to remove restrictions, I had 7 trade routes going, my Taxes were at 5%, global approval was 100%, and I was still making 3000 bc a turn with a HUGE army. It was like having an endless Economic Boom event.

If you get the above, however, do not go Evil. The U.P. also has a vote to restrict Evil trade. This happened to me. I recovered from it, but it's just not the same.

Thanks guys. It's a big old game and I have much to learn.

So most of the early turns are spent building ships to explore, colonise and mine?

To mine, do I just send my miner to the 'rock'?

That's right: your flagship can explore as well as survey anomalies (I usually double-click the flagship and set him to auto-survey so he'll automatically head for nearby anomalies without you having to guess where they are). The space miner essentially 'builds' mines on asteroid fields: just move it onto the field and you'll see a building timer come up if you did it right.

One correction to your statement though: most of the early turns are spent building ships to colonise, period. One space miner is good enough early on, and the game's default scout ships are pretty useless (they lack the ability to survey anomalies), so just keep pumping out those colony ships!

Also keep in mind that there's no single way to manage your economy in the early stages... Vidszhite's tactics are perfectly fine but I tend to use a very different approach in the early game, building quite aggressively even on newly-colonized planets. It's a much trickier economic balancing act, but if I pull it off, the moment I have a working economy my entire empire's infrastructure is all up and running. But when it comes to finding an approach that suits your play style you should have a working knowledge of the mechanics of the game... for that purpose I'd also strongly recommend the galciv wiki for that; it helped me IMMENSELY when I was just picking it up.

Whichever approach you take, here are some things I found useful for keeping my economy afloat in the tricky early stages:

- Trade. Not just for the freighters, but for the economic capital building. In the early part of the game, a properly-placed economic capital can single-handedly pay for your entire civilization even with another 4-5 planets hemorrhaging money.

- Research sensors as early as is convenient. In the early stages anomalies will be a big source of income, and once you have sensors you can build ships with the survey ability. On top of my starting flagship, I try to have 1-2 more tiny-hulled ships with a survey module so I can grab more anomalies than my rivals.

- Tech trading. You'll notice that certain techs give certain stats a permanent boost just by researching them. e.g. planetary improvements opens the way to build a bunch of buildings, but also gives you an empire-wide bonus to production and research the moment you research it. Some other races you'll run into have unique techs that give them significant bonuses to these stats; I try to get these techs from them no matter the price, especially if they yield economic or morale bonuses.

I thought there was a difference between basic farm and xeno farm

I would rely less on trade as the game progresses, and races get eliminated, especially if you have no alliances.

When I first started playing, I relied heavily on trade routes...built econ starbases all along them to max out the income. But I found that I could not cover expenses and turn a profit without the trade income...a bad idea when everyone turns against you.

Now, I make sure I boost population high enough, build a number of stock markets, and increase my influence to the point of getting a tidy bit of income from tourism. The income from those three sources meets or exceeds my weekly expenses, and trade is extra on top of that. A much more self-sufficient way to go, IMHO...

The difference between basic farming and Zeno Farming is...basic farming feeds 3 billion, Zeno Farming feeds 4 billion.

"The difference between basic farming and Zeno Farming is...basic farming feeds 3 billion, Zeno Farming feeds 4 billion."

This is my point. I have to research Xeno farming to build a Xeno farm but can't build basic ones.

IIRC, first you must research Xeno Engineering, and then Planetary Improvements. In any case, these should be the first two techs you research anyways..............