gear shifter is loose

Depends on the cause. There is a pivot pin that holds the shift lever in place that could be broken. The spring that gives the lever its feel could be broken. There could be a broken or worn bushing that part of the shifter linkage is mounted to. Brackets bolted to the body or transmission could be rusted away. You need someone to look at it and watch what moves when you work the lever.

Do you mean the lever itself is loose or is it more like you can move the lever up/down and the car does not shift correctly.

The second one is usually caused by the shift cable bracket bolts getting loose. Very common.
If this video looks like the same problem, the solution is likely the same.
https://www.youtube.com/watch?v=LKqiDy_Po2M