Dispay ad, Clicks or Conversions

I was hoping someone could tell me if choosing Clicks or Conversions is best for my bidding strategy when I place a Display Ad? I was told choosing Clicks is best for Search Ads.

Also, whats the advantage of choosing one over the other? and how does google charge me if you choose conversions? Getting charged per clicks is pretty self explanatory, but how does google charge me for conversions? does someone has to click/navigate different areas of my presell in order to get charged?

I still can’t seem to grasp the bidding strategy concept, specially the conversion options
Thank you