Middle forms of verbs strong and weak

I just about finished the final lesson in the Norse Course and I was looking at the middle forms of

different verbs,both strong and weak.Could someone define the middle forms of a verb?

The primary course does not cover many topics such as the above,the past tense, the subjunctive tense both present and past and other topics like weak nouns,feminine nouns,etc.

 

It must take years to absorb much of all this detailed info.

 

I am only a recent participant and would appreciate any comments.

 

                                                        

                                                                 Ed