There are countless reactions involving alkenes cited in the literature. This and the next page is but a brief summary of the most common ones that are used in introductory organic textbooks.

Reaction of alkenes with hydrohalic acids
Without peroxides, halide ends up on most highly substituted carbon.
With peroxides, halide ends up on least substituted carbon.

Oxymercuration/Demurcuration
This reaction yields the Markovnikov product, with the alcohol on the most highly substituted carbon.

Hydroboration
This reaction yields the Anti-Markovnikov product, with the alcohol on the least substituted carbon.

Catalytic Hydrogenation
Bubbling hydrogen gas over an alkene in the presence of a metal catalyst causes reduction forming cis hydrogens.

Bromination
Bromine adds trans across the double bond.