This bind needs to be placed in your autoexec, or used each time you reopen CS:GO. This bind will cause you to jump and throw the grenade you are currently holding - useful for smokes that require a lineup. You need to hold down left click (causing your character to pull out the pin) on the grenade and then press your bind key.
Find the commands for this bind below. Note that you need to pull back the grenade (hold left click) and get ready to throw before hitting your bind key.
The first part of this command creates an "alias" - a shortcut. The alias +jumpthrow actually runs two commands. The first command is +jump, which makes your character jump, and the second is -attack makes your character stop attacking (so that you throw the grenade you have pulled back). The -jumpthrow alias runs the -jump command which always needs to be ran after using the +jump command, so that you can jump again.
The second part of this command binds those two aliases to the ALT key.