Can't install mac os X on my MP

I tried to copy mac os x installation app that I downloaded from apple website and put it into a USB disk and plug the USB disk into the macbook.

That won't work. Create a "bootable USB installer" by following these instructions on a working Mac that is capable of actually running OS X 10.13.x "High Sierra" or earlier macOS version: Create a bootable installer for macOS - Apple Support.

There are "early" and "late" 2011 model MBPs. If yours is the "early 2011" model then reinstall that Mac's originally installed operating system using the original grey System Install DVD that came with it. That would have been Snow Leopard. Then, update it using Software Update, and upgrade it to Mountain Lion or any later version up to High Sierra. If your Mac didn't come with that disc, or if you cannot find it, lost it, don't have it, etc your options become limited in a hurry.

If yours is the "late 2011" variant then it shipped with Lion. There are no DVDs for it, but you may be able to reinstall Lion by booting the Internet version of macOS Recovery: hold ⌘ ⌥ R upon startup. Be advised that there are many anecdotal reports Apple removed that option about a year or so ago, leaving only the alternatives described above.

To add to @John Galt's excellent advice.....

In order to create a bootable macOS 10.11 or 10.13 USB stick, you generally need access to another compatible Mac from:

• Late-2009 to 2018 to create a 10.13 High Sierra installer
• 2007 to 2015 to create a 10.11 El Capitan installer

You can use the information in the following article to confirm the other Mac is compatible with one of these two operating systems since the model years give are just a generalization:

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

Those other compatible Macs can currently be running any version of macOS 10.6+.

AlexTheAppleBoy Said:

"Can't install mac os X on my MP: There is a problem with my Macbook pro 2011. I erased the SSD and I can't install Mac os X mountain lion. it says 'This copy of the install OS X Mountain Lion application is damaged, and can't be used to install OS X'[...]"

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If Mountain Lion is NOT a "Must"...

Set this Up Using a Snow Leopard Disk:

Perform this install using a Snow Leopard disk. You'll likely find one on eBay. They are become harder to come by as time proceeds. Most vendors on Amazon have run out.