how to run and play minecraft for free in ubuntu 18.04

first you need to uninstall java9 and java10 , because the launcher which i am going to show you guys will only run with java8 . so run these commands to install java8 in ubuntu -

sudo apt-get install openjdk-8-jre

then ,

sudo apt-get install openjfx.

now you need to download a launcher from https://tlauncher.org/ and go to files and right click the downloaded file click on extract here and now open the extracted file , again right click the file and now click on permissions then click on "enable file execution as a program". then a bit later the launcher will open and you need to click on install files and when the files installation is complete hit "enter game" or "play game" and then minecraft will be launched. if you did not understood it well then see the video down.