1. It's all about pattern matching, as a lot of math is.
Letter A corresponds to letter J, as both are first in the names of their respective triangles.
Letter B corresponds to letter K, as both are second in the triangle names. Likewise, letter C corresponds to letter L, as both are last.

Realizing this, it should not be too much of a stretch to see
∠B ⇒ ∠K
∠C ⇒ ∠L
AC ⇒ JL
BC ⇒ KL

2. Same deal. Match the patterns. Here, you're counting rings in the angle marks.
1 ⇒ 1, so A ⇒ R
2 ⇒ 2, so B ⇒ Q
since the figures are reportedly similar, you can continue in the same order to finish.
ABCD ~ RQPS

3. The marked triangles cannot be similar. There are a number of ways to figure this. Basically, you want the ratios of sides to be the same for any similar triangles.

Here, you can eliminate the marked ones because the short side is too short relative to the others. (The average of the other two sides is double the short side in the similar triangles.)