I am trying to reinstall OS X on a MacBook Pro that i purchased however it takes me to a screen to install OS X 10.11 and I click continue but then it says a required download is missing. Can I please have some assistance?

Did this mac that you bought not have an OS installed on it?

If you have to use the Recovery Servers then read the following. If it does have a functioning OS you can skip to the

information under the dashed line.

The certificates for several of Apples OS's expired in October 2019, Apple have been very poor at getting these updated on their Recovery Servers with valid certificates. This may be the problem you are experiencing. 

Try this workaround, we are going to set the time and date on your mac to a date previous to the expiry date of the certificates.

Connect your mac to your router via cable, not WiFi

Boot to your Recovery HD, click on Utilities in the menubar select Terminal.

Make sure WiFi is switched off, it can reset the date back to today.

Enter a new date, for example or just copy and paste

sudo date -u 011421002015

press Return

enter your password

press Return

If Terminal returns an error saying sudo : command not found, then try again without sudo.

Now try downloading the OS.

If this works then when the OS is installed and booted up you can Open System Preferences> Date & Time

and reset the time back to today.

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Read the following. You do not need to reset the date and time for this.

How to upgrade to OS X El Capitan – Apple Support

Go to Section 4 and click on Download OS X El Capitan.

This downloads InstallMacOSX.dmg to your Downloads folder.

When downloaded open to InstallMacOSX.pkg, double-click on

that and an installation window will open, this does not install El Capitan

but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which

you will find in your Applications folder, it should be 6.2GBs in size. 

If the installation window asks which disk you want to install to, you must pick 

the disk that you are booted to at the time. Not any internal or external disk that 

you want to eventually install El Capitan on, that is for later.

To start the installation of El Capitan double click on the Install OS X El Capitan.app.

The copy of the install app self deletes after installing El Capitan, so make sure you keep a copy of the InstallMacOSX.dmg

if you need it in future, or you could just make a copy of the Install OS X El Capitan.app prior to installing and moving it to

an external drive for safe keeping. It is also possible to create a bootable USB installer disk, using the Install OS X El Capitan.app

in the Applications folder, and the createinstallmedia command in the Terminal app. 

Read the instructions here,

How to create a bootable installer for macOS – Apple Support

We are all users like yourself so we cannot connect to your mac, especially if it has no OS.

At the top right of the screen you will see Contact Support, click on that and see if you get anywhere.

Just answer the first question did the MacBook Pro come with an OS installed on it.

If so which OS is it, and what model and year of MacBook Pro is it.

No it doesn't answer my question about whether or not it came with an OS installed on it, it should have.

Where did you get it.

Follow my instructions for downloading El Capitan from the Recovery Servers.

It should have come with an OS installed on it.

Do you have another mac in the house or can borrow one, if so you can do the second

part of my long post, but it needs to be done on a mac that can run El Capitan.

Once you have got Install OS X El Capitan.app in theApplications folder of the

other mac then you can make a bootable USB stick installer.

Use the USB to plug in to the MBP and restart while holding down the option/ alt key.

When the Startup Manager screen show select the USB and press Return.

The mac will restart and boot up to the USB stick, you will see a Utilities panel

select Install OS X and press Continue.

The installer should start, follow the instructions.