The 1st, from left to right, is for snapping, which is useful if you want to align clips or a clip to your play head.
The 2nd enables audio scrubbing, so hearing the sound while dragging the play head.
The 3rd enables ripple editing, which makes it possible to move or insert clips in front of others and keep the gaps the same.
And the 4th enables ripple editing for all tracks, except locked ones, if you want to change more than one track.
(Differently worded explanations: Glossary / Terminology)
I would suggest you try each in an example project to actually get a feel for the functionality of each button.