Animation stuff is extremely visual-oriented so it is poorly suited to learning in a little text box like this.
Blend Trees are only one many possible solutions / tools, but you need to understand if they are even applicable to what you are doing. To this end, you must become intimately familiar with the entire animation toolchain so you can achieve what you need, and that will be done via tutorials for games or animation effects similar to what you desire.
Anything with Animations / Animators / Mechanim:
Only consider the code AFTER you have done this critical step:
Always start with the Animator state machine and prove it works in isolation, no code at all.
Here’s more reading: