Can communicate but not upload. HELP!

Ok so I am using Linux Ubuntu 18.04 and bought an UNO R3 to begin learning code. I downloaded the Arduino Linux32 1.8.13 IDE. Everything worked as it should until I powered off my PC and came back the next day. When I powered up Arduino would not open. I uninstalled it and found another installation method that worked. Now every time that I power up Arduno will load and run.

It will recognize the board and show it in a port. I can see the TX and RX lights flash and the program will read the boards serial number and such.

When I open "Blink" and verify it all is well but when I click on upload I get the following error:

Arduino: 1.8.13 (Linux), Board: "Arduino Uno"

Sketch uses 924 bytes (2%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
An error occurred while uploading the sketch
avrdude: ser_open(): can't open device "/dev/ttyS0": Permission denied

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

I have been through a ton of posts and tried stopping modemmanager and such but no luck. Any real solutions?

I am new to both Linux and Arduino so I am a total redneck in a world of greek language so please be detailed. Thanks

Have you made yourself a member of the dialout group?

After doing that, you have to logout and login again for the change to take effect.