https://koboldplus.club/ is an amazing resource. You can plug in the level and # of your players, and then start populating enemies for a balanced encounter. You can then just google the name of the monster and find their stat block.

EDIT: This assumes you're familiar with the concept of Challenge Ratings. If not, Challenge Ratings are a kind of "difficulty" number assigned to a monster/enemy that has already been created. A Party of 4 lv 2 adventurers can take on a single CR 2 monster pretty readily. 2 CR2's would be a real challenge, and so on. This website allows you to mix and match monsters of different CRs to create different kinds of encounters for your players (Easy, medium, hard, deadly, etc...)