Alkyl tosylates are alkylating agents because tosylate is electron-withdrawing as well as a good leaving group.  Tosylate is a pseudohalide.  Toluenesulfonate esters undergo nucleophilic attack or elimination.  Reduction of tosylate esters gives the hydrocarbon.  Thus, tosylation followed by reduction allows for the deoxygenation of alcohols.
In a famous and illustrative use of tosylate, 2-norbornyl cation was displaced from the 7-norbornenyl tosylate.  The elimination occurs 10 times faster than the solvolysis of anti-7-norbornyl p-toluenesulfonate.
Tosylates are also protecting group for alcohols.  They are prepared by combining the alcohol with 4-toluenesulfonyl chloride, usually in an aprotic solvent, often pyridine.