Not able to merge surfaces into solid. Need help identifying my mistakes please.

I am a new user of Solidworks. So any help you offer will be of great service and regarded very highly.

I am facing trouble trying to merge different surfaces (with minor gaps) into a solid. I tried many different methods out there on various websites, forums, tutorials, etc... but, so far, have had no luck. Can anybody please help??? Please can anybody tell me what am I doing wrong here? I know, for once, that there are a lot of knitted surfaces that I've created. Please guide me on how to go about reducing the redundant ones.

I've attached the part file here.

Thankyou in advance.

SolidworksParts And Features