Protonation is always your first step on E1/E2/SN1/SN2
Although forming an alkene from an alcohol is not SN1 nor SN2
It is considered an Elimination Reaction E1/E2
dehydration means removal of _________?
i'll leave that up to you, it should be easy to answer
SN1/SN2 is a substitution nucleophilic meaning to say you substitute the OH grp w/ a halogen to form an alkyl halide
E1/E2 is an elimination meaning your OH and another H (thats should give you a hint about the above answer) is removed thus a double bond is formed to form an alkene
you need to see your reactants and products first b4 you decide what reaction mechanism it is. There too many...good luck when you get to Zaitsev and Markovnikov
remember 2ndary and tertiary alcohols go thru E1 because the formation of the carbocation by the dissociation of the alkyloxonium ion is stable enough, and yes the 3 beta alkyl groups do stabilize the carbocation thru hyperconjugation.
primary alcohols always go thru E2 because the carbocation is not going to be stable enough to be a intermediate in the reaction.
also remember, E1/E2 are all considered Beta elimination meaning the hydrogens of the beta carbons which are directly connected to the alpha carbon is removed to form a double bond.