Un-used programs in Task Manager/Services

Many times, there are lots of programs which load upon the start-up of a PC - causing the PC to load slowly and have its memory max out.  Sometimes those programs are needed, sometimes they are malware, sometimes they are rarely used programs, and sometimes, they are just programs which have been set-up to run in the start-up file without knowledge.  Everytime I want to clean this up and remove those files, I am told I should look at a resource like Google to see what the program is used for and whether or not it can be considered as malware and/or whether or not it can be removed.  Is there a better way of doing this so I do not have to look at each one?  Is there a list of the "necessary" files anywhere? 

My biggest fear of using internet sites to search this information is that depending on which site you access, whether it be Google or others, sometimes the information is conflicting. Also sometimes the site is trying to sell you a program which either will replace the file you just deleted or will remove the file you can easily remove otherwise.  Can someone please direct me (and others) to a reliable source which can provide a list of the necessary files to keep in the system services folder, the task manager, and also identify the others which may appear in those lists with a simple explanation of what those files are for?  This would be especially useful for the Novice computer user.

Thank you.