Not enough info and I'm about to go to bed. Easiest is delete and start again. You need to constrain geometry better than tutorials tend to show. I have never seen someone show proper topological design in tutorials either.

The main issue in cad is always π. When there are problems, think about where π is potentially being truncated to constrain a vertex. All geometry in cad is built sequentially

If i understand you correctly, I suppose you come from another cad program. In freecad you can't select a shape of a drawing to extrude or pocket. Each operation like pad needs its own, simple sketch to extrude.

Here is the workflow:

• create scetch
• create rectangle (70*100) in it
• exit sketch
• select sketch and click pad, make it 30mm
• close and click the top face, create new sketch
• in the sketch create a rectangle
• get the top edge with the transfer tool
• make the 3 sides 10mm spaced from the border
• make the last side of the rectangle vertical to the right side of the imported line (select the point at the end)
• exit sketch
• select the sketch and select pocket
• make it 10mm or so
• exit, select the face and then click draft
• angle it the way you want

Should be done

I don't know if that helps or what your error is exactly, if you need more help please be more specific what you did and what did not work and what you expected to happen