So, if wanting to express the time that I start sleeping, I would say:
• I go to sleep at 11 pm every day.
• I go to bed at 11 pm every day.
You cannot say:
• I sleep at 11 pm every day. - WRONG
The same principle applies in the past tense:
• Last night, we went to sleep at midnight.
• Yesterday, the kids went to sleep late.
You cannot say:
• Last night, we slept at midnight. - WRONG
• Yesterday, the kids slept late. - WRONG - because it changes the meaning (i.e. The kids stayed in bed later than normal in the morning.)
It's also possible to express the moment in which sleep begins by using the expression "to fall asleep" (note the use of the adjective asleep). While "go to sleep" and "go to bed" are more general and intentional in nature, "fall asleep" can be more accidental or involuntary, but can also be used to describe any transition into a sleep state.
• I always fall asleep during boring movies.
• If Jen falls asleep one more time at her desk, her boss is going to fire her.
In the past tense:
• The baby fell asleep in her arms.
• Tim fell asleep at the wheel and crashed his car.
If wanting to express the amount of time that one spends sleeping, then English works as follows:
• The kids sleep for a half-hour after lunch every day.
• She sleeps 7 hours a day on weekdays.
And in the past tense:
• I slept for an hour on the bus.
• You slept very little last night.
The same is true for the quality of sleep:
• On a train, she sleeps like a baby.
• I haven't slept well this week.
Knowing this will hopefully allow you to sleep better tonight :-)