how do i recover deleted MP3/VIDEO??

For starters, you must stop using your Mac immediately! The more you use it, the more likely the now free space will be overwritten by new data, making recovery anywhere from difficult to impossible.

You're going to need a few things to recover the data:

1) An external hard drive you can install OS X to so you have some other drive to startup to.

2) Once you have purchased an external drive, restart your Mac and hold the Command+R keys to startup in Recovery mode. Launch Disk Utility and partition the new external drive as GUID, and then format it as Mac OS Extended (Journaled).

3) Now that the external drive is ready to hold a Mac OS, quit Disk Utility (you're still in Recovery Mode), and install OS X to the external drive. Be very careful not to choose the internal drive. You don't want to write to it.

4) Restart and boot to the external drive. Actually, when you're done installing OS X to the external, the Mac should restart to it.

5) Purchase either FileSalvage or Data Rescue III and install it to the external drive, which should also be your startup drive for the moment.

6) Run the recovery app and do a full search for deleted files on the internal drive. Choose the external drive as the location to save the recovered data to.

May be this question can help you:

https://discussions.apple.com/thread/6124324

Take it easy first. It seems you got 2 questions, I will explain your questions one by one here.

For your Mac question:

To make you calm down, the first thing I want to tell you is that your lost data can be recovered. But this situation you need to pay attention: After data loss happened, don't do anything on your Mac (Little Tips: It is similar to your storage device, any of them. Once you find data loss situation, don't do anything on it.) until you find a suitable method to get your data back.

If you keep operating your Mac, you will have no idea what you've done that does harm to your "deleted data" on your Mac. Yes, here I say the "deleted data" on your Mac. Actually the data is not really deleted but only the space of it has been freed up by the Mac operating system so that the new data can take place of it. This is the reasons I ask you don't do anything on your Mac 'cause you don't know which process will write new data into your Mac hard drive that your "deleted data" is deleted from. Here I bring you some tips you may need after you met data loss problem:

1. If you’ve lost a file, time is of the essence. As new files saved to Mac hard drive or storage devices, the original files gets overwritten. So do not use the drive or disk which your deleted files are stored before at all, until you have completed the scanning and recovery process.
2. The system crashed or the files loss situation happens occasionally, so remember build a backup for the files periodically is strongly needed.
3. If you meet the file loss situation again, stop using the Mac or storage device right now, use another computer to process the files recovery.
4. If your hard disk has enough space for storing the files, then there is no need to empty the Trash Bin quite often to avoid the wrongly deletion which makes the unnecessary trouble happens.
5. Try to call professional expert or use the free third-party software like Recuva or Puran, etc.

For Your iPhone Questions:

Sometimes the iPhone does not respond though you sync it with your Mac. (Mind has the same questions.) You can try to change an other data line or another computer to see what happens. But if it is your iPhone's problem, you'd better send it to the repair shop. Don't try to fix it by yourself. This may also help: https://discussions.apple.com/thread/4671473

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There is no way to recover from a system there?

Sorry, I don't know what you mean by "there". Do you mean the Mac's hard drive you deleted the movies and music from? If so, that's what I explained, in some detail.

To repeat. No, you can't recover the data while booted to the same drive. The odds only increase that you will overwrite the data you want to recover. It's impossible to recover any data using the software I linked to above without another drive or partition. Doing so would likely overwrite data that hasn't been recovered yet with data which has.

If you mean your iPhone, I didn't address that part of your first post at all. I don't know why it wouldn't respond, or what you even meant by "respond". Respond how? To what?

You say these practices are too complicated and I was a student, I guess you could say simply some more?

Where, and in what way did I even slightly mention your ability to follow my outline to recover your data? It's a straight forward, step by step set of instructions you need to follow to have the best possible chance of recovering your data intact.

If you have questions on the steps, or still aren't quite sure how to proceed, just ask. But above all, don't use your Mac for anything until you are ready to proceed with an external hard drive.