the role of " Intent lock " in transaction and concurrency
It is not that simple to understand without making your hands dirty and digging much deeper into the SQL Server locking. And yes, you must take into account the locking escalation as it is a completely different approach and while sometimes could be very useful, it has its own negative consequences

I would suggest reading All about locking in SQL Server where you can find a lot of details, explained in a simple and concise manner, that allows even the beginners to process this rather complex thing like SQL locking