The first clause is the preparation and 붙이다 is the attaching: buy the sticker and stick it on, make that part separately and attach it, tear them off one at a time and stick them on, print a face and stick it up. The computer term for paste is built the same way, from copying and then sticking. 붙이다 is the transitive one, attaching something; 붙다 is being stuck to something.