Is it Present Simple?

[Paulys]

Hi there, I'm back :)
So I have several questions about these sentence which is below.

Which one of these sentence is correct?

So. Why I had to use is but not are?

This server sometimes lag(s)

Which word I need to use lag or lags? and why?
I think that right answer should be lags because I need to proper the Present Simple tense.

Regard. Thanks.

[Tdol]

Which one of these sentences is correct?

You use is because you are talking about one.

This server sometimes lag(s)

Lags:
This server sometimes lags
These servers sometimes lag

[Paulys]

Thank you sir so much. Regard.

[5jj]

So. Why I had to use is but not are?
So why did I have to use is not are?


Which word I need to use lag or lags? and why?.
Which word do I need to use, lag or lags? Why?

5