This is a really simple way of creating tesellating or tiling patterns in photoshop. After creating the initial square the pattern is saved by chosing the options Edit> Define Pattern. The tile can then be used as a paint bucket fill by choosing Edit> Fill> Use: Pattern, before choosing your saved pattern from the drop down menu. Any defined patterns will be saved in this list for future use unless you choose to delete them (Edit >Preset Manager > Patterns > Select & Delete).