Most training programs include exercises with 8-12 repetitions for several reasons.
Firstly , it is important to lay the foundation before proceeding to the development of maximum strength. Take moderate weights that are heavier than those you previously lifted, but not so heavy that your set stops two seconds after the start. Secondly , such a training does not take much time. Thirdly , despite the fact that the main effect of such training is muscle growth, it slightly affects everything: both strength and endurance.
And the last: most of the exercises in this version are safe for healthy people, while too heavy weight can overload the muscles.
First, select a weight that you can easily lift once, but don’t know how many repetitions you can do. If you get tired in less than 8 repetitions or, conversely, you have too much energy left after 12 repetitions, rest a couple of minutes and repeat with a different weight (lighter or heavier, depending on how the set went). Repeat until the weight seems suitable for you: it should be difficult, but doable.
If you find the right weight, repeat the same exercise with the same weight after a few days.
This will allow you to lay the foundation, improve your shape and understand whether you need to add weight in the near future.