So you want to know what RAM and CPU usage is?
RAM = Random Access Memory - It stores files on your computer, information about open files and folders, allowing you to access them quickly when you return to the app/file. The higher the RAM you have, the faster your PC will be. Having, say 512MB (Half a gigabyte) of RAM on Windows Vista would be very sluggish, the performance would be terrible, as Vista hogs so much RAM, which is one of the reasons why Windows 7 was released, to fix the mistake they made with Vista's high resource usage.
http://en.wikipedia.org/wiki/Random-access_memory
CPU = Central Processing Unit - This is basically used to carry out instructions, or commands as you may like it to computer programs.
http://en.wikipedia.org/wiki/Central_processing_unit.
The best way to know if something is wrong or not is by opening Task Manager (CTRL + SHIFT + ESC), clicking on the processes tab and searching for processes that you don't recognise or don't think you need. For example, I have 'avgtray.exe' running on my PC, which is for my AVG Anti Virus and that basically scans my computer for viruses and spyware.
If you see a process you don't recognise, go to a search engine and search for the process name to see what it does. Some processes are more obvious than others, i.e. firefox.exe is pretty obvious, same with keepass.exe (my password manager) and notepad.exe
If you don't want to go and try to eliminate infections or problems yourself, I recommend installing Malware Byte's Anti Malware which is one of the best free spyware scanners ever created, it finds pretty much any infection.
Sorry If I went into too much detail, or going offtopic, feel free to ask me if you need further help.