Yeah, the colours are random. It does gradually tell you what's what, but probably too gradually. I think they figured most people playing Chapter Zero would have played Gemcraft first. (
Original Gemcraft is a little easier, in part because instead of traps you just have water trenches.)
Going left-right top-bottom, you have:
Bomb: Costs no mana, does cost a gem. You choose this and drag a gem, and it explodes.
Mana Pool: Increases the total size of your mana pool, and the rate at which it regenerates, and the rate at which your score increases. Mostly useful for long battles.
Create Tower: Creates a new tower for placing gems in.
Create Trap: Creates a trap. A trap goes on the road instead of next to it. A gem placed in the trap will have a reduced primary damage effect, but increased *secondary* effect.
It took me a while to get the hang of traps. They're really handy for placing a blue gem in that slows monsters along the approach for where your towers are, and sometimes a green gem is good too. In some of the *much* later fights I've ended up with things like a many-trap sequence of blues and purples and greens on roads lined with towers.
Create Gem: Creates a gem, obviously. I seem to spend a lot of my time aiming to create gems at around level 3 or 4, but early on, when you don't have a lot of skillpoints available, do what you can, pretty much. One of the things to bear in mind is that often you're better off with two smaller gems than one big one, because of rate-of-fire limitations.
Combine Gem: Combines gems into a higher-level gem.
Also to bear in mind: Pure gems are, by default, stronger than mixed-colour gems. When you have enough skillpoints you can unlock Dual Gem Mastery, which buffs dual-colour gems, but just after that you get Pure Gem Mastery, so...
With practice you get used to the different gem colour effects and get strategic about what you put where.
With fights that include orange as an option, mind you, I will tend to restart the battle until my first gem is orange, because starting with a mana-steal gem makes everything easier.
One of the curious ironies of Gemcraft is that it gets easier the further you go, because skillpoints help a LOT. If you like, I can give you the load code for my savegame, so you can learn basic gemcraft skills while having some skillpoints to play with.