Here are some interesting puzzles that I came up with. If these aren't original and have come from somewhere else, please let me know.
The goal of each puzzle is to place dots on some intersections between two or more lines in such a way that each straight line, somewhere along itself, contains exactly two dots. Dots can only be placed at intersections. You should also do this in the way that uses the most dots possible. If the rules need to be clarified or if you have any questions, ask in the comment and I'll be happy to edit my answer.
Here is an example of a solved puzzle:
And here are some for you guys to solve: