When you do time trials in the original Super Mario Kart and you do well, you get to race against your ghost, so long as you race again on the same track. If you got a particularly good time on a track, wouldn't it be awesome if you could save that ghost to challenge yourself or your friends later on?

Good news for you, there is!

First, go to Time Trials and pick any track, preferably one that you're good at, and not Vanilla Lake 1. Next you have to qualify to have the game remember your ghost data. In order for that to happen, you have to not hit any walls, not fall off the track, not go into the water, and get a reasonably good time. I can't really tell you what the time threshold is, since it's different per track, but an easy way to check if you've satisfied all the criteria is to watch your replay. If you can use L and R to rotate the camera, then you've qualified for a ghost.

Then, when your replay is over, and you're looking at your options on what to do next, hold L, R, Y, and then press X. You'll hear a 'ding'.

Now, if you exit back to the menu where you choose your track, you'll notice that the name of the track has turned yellow, which means that you've saved your ghost.

Now just highlight the yellow track, and when it's asking if you're sure you want to race on that track, and hold L, R, X, and hit B. You'll hear another 'ding' and load your ghost data that you've saved.

Beware, though, you can only save one ghost on the cartridge. If you save another one on the same or another track, it'll erase the older one.