The verb propose means "to suggest a plan," like the most well-known thing to propose: marriage. If you propose to your girlfriend, you propose getting married, and you probably give her a ring, too.
The word propose comes from the Old French root words pro, meaning "forth" and poser, meaning "put, place." Using propose to refer to an offer of marriage was first recorded in the 1700s but the verb also has other meanings. It can mean to present for consideration or criticism, like proposing a four-day school week or "to nominate someone for an elected office or official post."