'Round up' means to look for and gather people or collect things together, eg

- I rounded my friends up for the wedding. (Meaning I gathered my friends)

- Please round up those books for me. (Collect/gather those books for me)

- Could you round up some information/some material for my research project? (Could you find and gather material for my . . .?)

Just as the sentences above indicate, 'round up' as a phrasal verb, which it is, is transitive (ie must have an object). You must mention the people or things gathered.

'Round up' also means to find and gather around someone in order to arrest them or do something to them. It is also transitive here. You must mention those rounded up.

- The police rounded the thieves up and interrogated them. (captured them)

- The thieves rounded the professor up with guns.

You don't use it intransitively, please (ie without its object), without mentioning what is rounded up:

- I need friends for my party. So I want to round up. ×

You should say transitively by mentioning the object (what is rounded up):

- I need friends for my party. So I want to round them up.√

However, 'round up' does not mean 'to conclude', which is what some people think and say:

- Mr Speaker, your time is up. Please round up. ×

That above is wrong.

To mean 'to conclude', you should use the phrasal verb 'round off', which means to finish an activity or complete something in a suitable way:

- Mr Speaker, your time's up! Please round your speech off. (Please finish or conclude it)

- You're still on this matter? Round it off!

Again, just as the sentences show, 'round off', like 'round up', is also transitive (you must mention what is to be rounded off or concluded or finished). Thus, you don't just say:

- You're wasting time. Please round off! I don't want to remain here. ×

That's wrong. You must mention what is rounded off:

- You're wasting time. Please round it off! I don't want to remain here. √

Remember: 'round off' is British usage. The Americans prefer 'round out'.

- You're wasting time. Please round it out! I don't want to remain here. (AmE)

Just learnt something today! Thanks.

Yes
Round up means collect, gather, arrest

Round off means end, stop.