Is Django Make Indexes for ManyToMany field?
It does for plain m2m fields - can't tell for sure for "through" tables since I don't have any in my current project and don't have access to other projects ATM, but it still should be the case since this index is necessary for the UNIQUE constraint. 
FWIW you can easily check it by yourself by looking at the tables definitions in your database (in MySQL / mariadb using the show create table yourtablename).
This being said, db index are only useful when there are mainly distinct values, and can actually degrade performances (depending on your db vendor etc) if that's not the case - for example, if you have a field with like 3 or 4 possible values (ie "gender" or something similar), indexing it might not yield the expected results. Should not be an issue for m2m tables since the (table1_id, table2_id) pair is supposed to be unique, but the point is that you should not believe that just adding indexes will automagically boost your performances - tuning SQL database performances is a trade in and by itself, and actually depends a lot of how you actually use your data.
i ask if Django make database indexes for ManyToMany Field ... and if yes is it do this for the model i provide in through ? 
i just want to make sure that database will go fast when it have a lot of data