I assume you have watched this tutorial:

http://www.youtube.com/watch?v=CNxfZwvaQ-k
That covers the basics using one of the 4x4 puzzles.

If you are really just getting started, hit the new game link until you see one that is a 4x4, has a relatively high solve percentage, and a relatively low average solve time.

Once you get past the direct true and false relationships and transposing the true relationships, you get to the next level where you have more indirect true or false relationships.

If A is less (or more) than B, then A cannot be B.

If A is either B or C, then, B cannot be C.

Of A and B, if one of them is C and the other is D, then A cannot be B, and C cannot be D.

If you get stuck, post the screen shot or provide the puzzle category labels and clues, and someone will walk you through the solution.

You might have done this already, but you can do a web search for "How to solve logic puzzles" to get even more tips.

Happy solving !