How to install figma or sketch in Ubuntu?

The short answer

To install Figma:

Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

sudo snap install --edge figma

If snap isn't installed, just do:

sudo apt install snap

If you get the error:

error: snap "figma" not found

Download the Figma snap package, and run

sudo snap install --dangerous figma_0.4_amd64.snap

You can use gdebi. If you don't have it installed, you can install it by running:

sudo apt install gdebi

Download either the 64 Bit, or the 32Bit version depending on your system.

Once installed, open the downloaded file with gdebi, and click on file --> Open Choose the package you've downloaded, and open it. Once opened, just click Install.

Edit:

The command for latest versions of Ubuntu should be updated. for 16.04 and later

sudo snap install figma-linux

Thanks to Fireball.1

sudo snap install figma-linux

installs the latest stable version (see https://snapcraft.io/figma-linux)