Most A4 sheets consist of two or three pictures to fit on an A6 card. There are also sheets with mini pictures, usually 9 on a sheet.
Cut out all the different pieces of one picture. Stick double sided tape on back of the largest picture and stick 3D Foam squares, which are available in different sizes (see Tools page), on the other parts.
I use on 'normal' pictures 1.5mm or 2mm squares, on Pyramid pictures 1mm squares, as there are quite a lot of layers. On single pieces or parts that need the extra height, I use 3mm. There are also Mini squares available - 2.5 x 2.5mm and 1mm or 1.5mm thick.
Assemble from largest to smallest piece(s). If you like you can also shape some pieces by placing it in the palm of your hand and shaping it with your finger.
Some sheets are numbered, which makes it easier for beginners to start with.
Have F U N!