The first place to start, is to have an idea. Think of what you want to simulate or prop to build. This gives you a goal to work on.
Wiper motors are easy to work with. Air cylinders get complexed and require an air compressor.
Then you will have to decide if you want an automatic or manual operated prop. Automatic will need a choice of controllers, there are many to choose from.
manually is operated by a simple switch, as is mine here in this forum post.
There is a lot of info on here to review.If you have questions, don't be afraid to ask. There are many educated and knowledgeable people here to help you and offer advice.
Always scarying the yell out of them