Alkene will react with H+ first to form a carbocation, which may undergo rearrangement if required to form more stable carbocation.

The carbocation is then attacked by H2O:, the lone pair of electrons on oxygen serves as nucleophile to form the oxonium ion, which will then eliminate a proton to form the alcohol.

 

 

CH2=CH2 + H+         CH3CH2+    +  H2O:      CH3CH2OH2+      CH3CH2OH + H+