extreme lag and crash

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What I expected to happen was no lag because this is a new computer .
Describe what you thought should happen here

What actually happened was it was extremely lag and It crashed me so many times and I could not do even a single punch.
Describe what happened here

Steps to Reproduce:
1. go to minecraft
2. then start playing on multiplayer.
3.go there for minutes and then it happens p.s if it is only some thing in my pc the I apologise for this ...