When I open Windows Task Manager there are a bunch of processes running.?

Yes, you'll find a number of processes always running in your computer. They are required for the Operating System (Windows, Mac OS X, Linux, etc) and other applications to function properly. Some are background tasks, like Print Spooler service (required for the print services to work correctly), some are service hosts (eg. svchost.exe) required for other programs/services to run properly. There's also your antivirus/firewall program running in the background. You need to keep these untouched.

You can close a few services however as and when you wish or even prevent them from running right from the startup of your computer.

1. Managing Startup programs: For windows, launch 'msconfig' from the 'Run' dialog. Go to the startup tab and deselect whatever you find is unnecessary. eg; Updater services for various applications. Go to the Services tab and deselect unnecessary ones like 'Windows Error Reporting service' but be careful here. You could use some help from google.

2. Kill applications which are not responding or have not closed fully. Like 'firefox.exe' when it has not actually stopped even when exited. Do this as you wish.

3. A good thing to ensure that your computer does not slow down is to correct file system errors by using 'chkdsk' (XP variant, chk what's there in Win 7). Also keep your system clean of temporary internet files and those in the temp folder (%temp%).

4. Another good trick is to keep the registry tidy by regularly using a Registry Cleaner tool.

Use http://www.tasklist.org/ to find out what is running and what you can stop. Generally anything by Microsoft is worth keeping up, but you'll find a lot of the other programs on your computer may be running in the background aswell which you don't need.