print help

at the moment just about got pla running but as in picture every so orten the layer does not fully make comtact e.g little gaps where can break

not tryed abs yet trying to get pla working first
any ideas its a small part not tryed larger yet

also in a previous post some one was talking about z wobble and checking lead screws what are these where are they
still a novice printer learned a lot of things on the way but i did something after havinfg some reasonable prints with abs and now in a mess again