There are two types of requests:
First, we show you requests from your connections. That's only contacts who also have you as a contact. This makes sure that requests are shared between people that already trust each other.
You can reply directly to these kinds of requests. You can also make an introduction to one of your contacts or connections that might be able to help.
Second, we show you requests from the connections of your connections. When posting a request, your connection can decide to share their request more broadly for maximum effect.
Since you don't know these people yet, you can't reply to them directly. You can ask your connection to introduce you instead. It's the best way to meet a new person; through mutual friends.
You can switch between the first and second type of request by using the filter button on the top left of the Request screen.