The first of this series is the active present participle, also called the VA-participle. It's used to replace joka-sentences as well as että-sentences.
If you understand the basics of postpositions, this is the right place for you Learn about the inflection of postpositions in the mistä and mihin form!
Finnish has a lot of postpositions. Especially the concrete ones that are related to where something is situated are important, but there are many more!