Some mobile apps will match you with people based on criteria, including age, gender, and geographic proximity.
More traditional sites may offer anything from a simple search to a highly specific advanced search.
Depending on the dating site, all other members might be able to see your profile and message you.
Check to see what safeguards are put in place by the site, and which ones you can enable to limit those who sees your profile.
Online dating has grown in popularity to the point where there is almost no social stigma attached to it.