To toast, cheers, or touch glasses of any type of alcohol together with your drinking partner(s) in the spirit of goodwill, health, luck, or congratulations.

In many cultures, it's considered to be good luck to make eye contact when doing so (and bad luck not to).

Some people also follow a tradition of tapping the bar with the glass after clicking glasses (and before drinking) to express fondness for the business/bar and the people who work there.

Brazilian butt lift

I've also heard it's a show of good faith i.e. no poison in others glasses as clinking together would mix the poison into yours.