MyBB Community Forums

I want to migrate my forum from phpbb to mybb. If I do that then will I be loosing my topics and threads? And also I don't want my urls to change as many of them are already indexed in search engines so is that possible. 

If any body provide me detail of doing this migration then it will be really helpful (videos are also preferred.)

Take a look at Merge system
https://mybb.com/download/merge-system/

For keeping the existing urls, if it doesn't match you may need to be using detailed rewrite rules via .htaccess or may be a router in complex case.