Hi,
I would strongly recommend that you do the embedded tutorials in the Fusion Documentation and also some of the
Self-Paced Learning to help you to learn fusion faster and better. They can be found here:

It is also much easier for the forum to help you if you attach your file AND a screenshot of what you want to achieve
and what the problem is. You can create a file to export like this:

Time spent on the tutorials and self paced learning will not be wasted.
A sketch is fully constrained when the small lock icon appears next to the sketch in the browser tree. Based on the
sketch you have drawn already, the missing constraints will be the length of the vertical line so that the tangent line
has a definitive point to join to.

You will see that as soon as the length of the line is defines to be 62.5mm (or some other value), the tangent line
length can now be calculated by fusion. This makes the sketch fully defined and the lock icon is now on the sketch.
A useful tool is the Sketch.ShowUnderconstrained Text Command. If you type it into the Command Line it will show
all unconstrained lines and points. Remember also to hover your mouse over black lines and their intersections. A
line that is constrained will turn black but if the point on the end is not constrained it will be a white circle instead of
a black one. Many a beginner has been caught out by this.

I am sure Coursera has a good program and I encourage you to continue with it. I would also strongly suggest you
check out RULE #0 that is pinned to the forum about how to learn fusion. It will help a lot.
Cheers
Andrew