A good jab is the single most important punch.
In defense, it forestalls the opponent's attack. In offense, it is both punishing and sets up other strikes. Used properly it is the safest punch to throw and limits the opponent's ability to counter especially when you learn to double up your jab.
It manages distance and disrupts your opponents timing. It is also an extremely effective counter punch as you apply the lessons of footwork and head movement.
Practice on the bag if you have access to one or shadow box if you do not.
If you are sequestered at home during this time, any open space will do for practicing what I am showing in these videos. Drill these basics, they are the foundation for everything else.