Another Student written Handout. This is written by Rohan Goyal, IMO bronze Medallist from India. You should first begin with getting comfortable using ideas like Vieta's formulas and others on problems. If you are comfortable with these and can consistently solve A1-A2 level problems on ISL.(IMO Selection Tests) I recommend reading his handout.
It's not written in the best way and is hard to read at times and is quite dense as it covers a lot of ground over just 50 pages so please be comfortable before getting into it.
The above PDF is a work of Rohan Goyal, so all credits to him. Cheers!