Introduction
The lesson video is the following
Main position
In this lesson we have seen how to invade in the following situation.
White has only one answer.
From there black can choose A to get strength outside. B for a crazy ko fight in case black has a lot of ko threats or is behind and needs to find something. Finally, C is territorial.
Invasion at A
The following sequence is usually played after the invasion at A.
If white tenuki, then in the future black can force all the moves to 7, and 7 is sente because it threats to start a big ko.
Invasion at B
Black B leads to a big ko that should not be played unless black has a lot of ko threats or if black is losing and want to create complications.
Invasion at C
Black C is a territorial move. Usually, white will connect and black will then connect also.
If white tries to cut, then black jumps out and split the two groups. It should be an alright fight for black.