How to add edge between two vertices? I am in desperate need of help again. 

How do I add edge and one vertex between two vertices in Blender 2.8?
I put a red dot where I'd like to have the new vertex =).

Thank you so much!!

Best regards 
Sophie
To make an edge between two vertices press F. If the vertices are on opposite sides of a face you can instead use J (for join).

To add a vertex, select the edge. Use Subdivide from the Edge menu.

To slide the vertex along the edge double press G.