Fillet betweet 2 solids

I am a new user. I have a project for school and I have tomake an part.
The making of is it going pretty well, only I have 1 problem:

I want to make an fillet between two sections of parts. I've triedeverything, but just can't figure out how it can be done.
I have attached an image of what I mean exactly.

Could anyone of you post an sort of "walkthrough" for this problem?

Thanks in advance fron the Netherlands!

JoostSolidworksParts And Features