How can i make picture collages?

I think the title was a bit confusing. I would like to make different collages on the internet with picnik, or some other picture website but i want it to look cute and not just that i'm trying to hard to be cool. for example my friend made a four picture collage of picnik and one section had her in a winter jacket, the next section had her in a flowery skirt, the next had her in shorts, tank top and sunglasses and the last one she had her backpack with her and she labeled each section in different fonts, winter, spring, summer, fall. i thought that was quite cute. do u have any other ideas for collages or just pictures with friends. another example is i took a picture of all my friends sitting on the back of a shiny red truck at the beach during a sunset. it was awesome!! plz help name some collages, friend photos and places where i can do them like picnik or what not.