Windows is more resource intensive than previous versions of Windows that you might've ran before Windows 10.
If you upgraded your computer from another operating system to Windows 10 then make sure you have more than 1 GB of ram installed since even if Windows 10 states that Windows 10 will run on a minimum of 1 GB of ram it will run slow.
For optimal performance of Windows 10 operating system you should have at least 4 GB of ram installed in your computer which you can easily upgrade by going to ebay and purchasing ram sticks for your desktop computer and installing them.
8 GB of Ram would be even better for Windows 10 but 4 GB is what you should at least have so your computer won't slow down and crash.
If it's not that then make sure you don't have too many unwanted or not needed programs running in the background.
You can hit the CTRL ALT DELETE keys at the same time to bring up Task Manager where you can find processes and applications that are running and stop them if not needed.