For the dihedral group( ) with { }

(3) Find ?

(4) What are the left cosets of ?

(5) Prove if is normal.

(6) Construct the Cayley table of

I've tried really hard to work these questions out. I worked out the first two questions (from the attached image above) but I'm having trouble with the four posted here. I really need to be shown how to do these otherwise I wont get it. Ive been working on these for about 6 hours and Im not getting anywhere.