Then check the codex for Biochem and it will tell you which gathering materials to pick up. Those gathering skills get you materials to make biochem items. Each mission tells you what you'll get out of it. Bioanalysis and if I'm not mistaken, Diplomacy are the 2 that biochem uses.
Take a crafting skill, then check the codex. It tells you which gathering skills compliment each crafting skill. It's best to take them so you aren't buying materials for your crafting skill. You can then sell the extra materials you don't use for credits.
No Problem, it's like the first thing I turn on when making a new character. It might be in the user interface options, not sure, but it is in there somewhere.