The Silent Realms are sections in The Legend of Zelda: Skyward Sword that are very similar to the parts in Mario Sunshine in which you didn't have Fludd. You are placed in an alternate universe without Fi or the Master Sword and you must escape this place, in order to do you have to collect Tears like in Twilight Princess. Once you collect all the tears you will return to the world of the living and you get a prize.
There are three elements in the Silent Realms that are relevant to your task:
The tears which are the items you need to collect, they are very easy to recognize due to their shape. Collection a tear will freeze the Guardians (more on them later) in place for ninety seconds.
The fruit which shows the locations of the tears in the shape of a beam of light going into the sky for about half a minute. They look a bit like white apples and are located all over the map, but they are rarely hidden like the tears are.
The guardians which are enemies. They are frozen in place, but they will give chase the second you step out of the safety circle. They can be frozen back when you find a tear, but once time runs out or you touch a pool of water they will activate again. One hit from these guys and you will return to the world of the living without receiving your prize.
What you are going to want to do is getting the tears without the Guardians waking up at all, the best way to do so is by picking up the one at the start and then rushing to the nearest fruit. Now you can see the location of all the tears, look for ones that require you to climb something and go for those first, if you find one located near water or placed somewhere you can't reach it normally you should get those too. The reason for this is that these tears can take a lot of time to collect and it is easier to run out of time and quickly get one of the easier tears than to run out of time and having to quickly reach a difficult one.
If you do have to face off against the guardians it is key to remain calm, if you run around like an idiot they will make quick work of you. Know that if they will get you it doesn't mean anything besides that you will have to start the realm over, you are not killed and you don't lose anything. When the guardians are activated they will only chase you if they see you, so stay clear of them and try to get a fruit or tear as soon as possible, then rush for the nearest/easiest tear you can find and resume your business. Do not try to fight the guardians, they can't be harmed or destroyed.
There are several occasions during which you will have to enter the Silent Realm throughout the game, they will increase in difficulty, but if you stay calm and follow these pointers you should be fine.