Writing competitions are a way to win money as well as promote your brand as an author. They range from prose to poetry, and may or may not have a specific theme. Some may also publish anthologies of winning entries.
It is usual for writing competitions, smaller ones in particular, to charge a fee per work entered. This usually goes towards the prize money and the admin fee.
Many writer sites keep an updated list of competitions, so we’ll refer to you to their helpful resources: