Focus is the ability to hold a concept steady inside your mind.
Of course it’s not that complicated, if circumstances allow, nobody disapproves, something very urgent doesn’t come up, life doesn’t offer more tempting alternatives, you don’t encounter resistance, your mental wheels don’t spin so fast you can’t even hear yourself think, it doesn’t threaten your comfort or unsettle your current circumstances, you don’t have to wait for the result, it’s not a low priority, the list is basically endless.
Focus is very simple in theory: you decide what you want to do and keep that goal front and center in your thoughts.
In practice, I wish you the best of luck.