i have 5th level paladin and dont know how can i cast his 2 spels from spel book

You first have to memorise them(for level 1 spells you have to have Wisdom of 11, for level two it's 12 etc up to 19), and then rest for them to become available and then click on he icon that looks like this :.) only upside-down. If that one doesn't exist, right-click on an empty slot on the toolbar and choose the icon then.

Also, IIRC paladins don't get level 2 spells until level 10.