What techniques do you see in these examples?
What materials do you think they used?
How have they used texture?
Don't overthink your idea before you even start! You will be creating and deciding what to do as you go.
Choose a paper size (minimum size is 9"x12" but 11"x14" gives you more room to play).
Start your base to work on by adding color and texture to your paper with gesso and acrylic paints. Work in layers until you're satisfied with color and texture.
Now choose 1 or 2 images from a magazine to get started.
Use matte medium to attach your first pieces.
After everything has dried mess it up! Use paint, pencils, chalk pastels, etc, to make some marks. Don't think too much! Just make some marks.
Now sit back, look at your art, and decide what to add next. Each time you add something new repeat steps 3 through 6. Add a little, make some marks, adjust, and keep going!