Spell slots in 5E are a unique mechanic that can be exploited to your advantage. In general, each spell slot has a certain number of uses that are determined by the spell’s level.
For example, a 1st-level spell has three uses, while a 5th-level spell has five uses. However, there is a special rule called “spell stacking” that allows you to use a spell multiple times in a single round, provided that the spells are of the same level (or lower).
This means that if you have two 1st-level spells that you want to use in the same round, you can do so without having to worry about using up your three uses for the spell at 1st level. Instead, you can use both of those 1st-level spells and then use your fourth and fifth levels for other spells.
In this way, you can potentially stack multiple 1st-level spells on top of each other to increase their effects.
However, there are some limitations to spell stacking. First of all, the spells must be of the same level.
Secondly, if one of the spells requires an action to cast (such as fireball), then the other spell cannot be cast until after the first spell has been completed. Finally, if one of the spells requires concentration (such as charm person), then the other spell cannot be cast until after the first spell has been completed.
So while spell stacking is an effective way to use your spells more effectively, there are some limitations that you must be aware of.