Q: How can I get rid of App Store? It keeps interrupting my work. I find App Store useless.

Have you tried closing the App Store app before you reboot?

If you're being haggled about downloading El Capitan because you're using Yosemite or below, just download El Capitan and keep the install file in your /Applications folder. The haggling should stop.

System Preferences -> App Store -> switch off everything.

But what do you mean exactly by "Every boot my desktop is redirected to App Store"? Be as specific as you can.

I run Mavericks and I don't get the App Store with every boot. You must have some preference setting somewhere telling your computer to do that.  I can't say which one but I systematically went through every single preference setting when I set up this computer 2 months ago.

Turn off Notifications for Appstore (in SystemPreferences-Notifications)