Prepositions give extra information on expressions. It is a part of speech that shows location, time, place, etc.

This does not indicate it is close to adverb; they are different.

Examples of prepositions: about, around, above, in, at, by, beneath, against, among, anti, along, below, down, during, instead of, according to, apart from, ahead of, etc.
Ex. 1. The bag floated on the river.
2. Put the food in the fridge.
3. Amaka was praised by her boss.
4. We should see her on Wednesday.
5. My friend lived in Bahamas.
6. We can take a walk instead of going by bus.

Note that instead is an adverb, while instead of is a preposition.

Like every part of speech, prepositions are often misused.
Note:
* Don't use 'discuss about', just say 'discuss...'1. We discussed the vision of the organisation.

* Some grammarians believe 'died from' is incorrect. However, 'died of/from' are both correct.
1. He dies of/from cancer.

* 'On the bed' means on top of the covers.
'In bed' means under the covers.
1. Tope is sick, he is in bed.
2. When you are tired, just lie on the bed and close your eyes.

* Use 'good at' not 'good in'.
1. I'm good at English but I'm bad at Maths and I'm terrible at Chemistry.