I need help in landing

The best way to learn is to start at the begining
Start off in a small plane and take the inbuilt lessons

Each aircraft has a different take off and landing speed,so we need to know what you are flying

I, and many others here, will recommend you take the FS lessons which cover and explain all the basic aircraft operations. Run them a few times and try to understand what's happening and why, as you make changes to the aircraft configuration.

There is also a huge personal reward in being able to fly and navigate manually; Much more than sitting watching the aircraft respond to an autopilot. What will you do if the autopilot fails?

It's really worth taking the time to fly and learn from the lessons. What you gain from them will greatly increase your enjoyment of the simulator.

I recommend taking the lessons and starting with a small aircraft. First learn how to land with a visual approach in a small plane, before going onto bigger aircraft and ILS landings. In your kneeboard under the bottom tab on the right, it will show what the aircraft glide speed should be at, while approaching the runway for the final, and what your flap settings should be. On your final approach if the runway has them, try to keep the lights at the begining of the runway to be on red over white. White over white means your coming in to high, and red over red means your to low.

As for your plane descending quickly, make sure you have your flaps set to the correct amount, as flaps will allow you to fly slower, keeping your plane level, without having to point your nose into the air to gradualy glide down. And when your just above the runway remember to lift your nose up a bit, and slow down your descent rate.