How do I enter combat in Mass Effect?

You are an infiltrator, you aren't supposed to be able to tank enemies. I don't know exactly what skills you've allocated, but here are some things that may help you out:

1. Put some points into electronics, each point gives you a boost to shield strength.
2. You can try assigning more points into tactical armor until you can wear medium armor.
3. Your weapons are pistols and sniper rifles. Stay in hiding, and pop out to shoot a single shot against an enemy (try to go for a headshot), before going back into hiding.
4. If you have enough points into electronics, you'll unlock damping which can stun enemies for a short duration. Also, try starting out fights by using overload to quickly take out enemy shields.
5. If your shields are down, stay under cover until it recharges, or you will die very fast.
6. Try to use tankish followers, such as Ashley.

Now, against the Fist fight, he will never wander out of his room, so you can just use the side of the doors for cover and pop out, shoot 1 turret, and then retreat until your shields come back up.

LOL this is funny. Exactly in this moment I'm playing Mass Effect 1, Infiltrator, Survivor.

At the beginning, the game is a bit harder because you got low skills. Use pistols + marksman and assasination + sniper. As yx said, you should go for medium armor.

yx is spot on. What I can tell you however is this: don't worry, the game will become more fun as soon as you reach about level 10. The Infiltrator rocks. You become extremely powerful later, I believe this is a late-game character, but I may be wrong (maybe all characters get very strong late-game, but I think that in the case of the the Infiltrator, this is more pronounced).

Don't despair, keep at it. Mass Effect rocks ::- D.