How to add another drive

First you need to confirm that you have an extra SATA port on your mother board, this will be the connection that is going from your original hard drive(HDD), to the motherboard, if there is another one that you can use for a new HDD the connection will be there

Second acquire your new drive and install it into your new PC, i would suggest to try to find somewhere in your PC if you can find room to place the drive, I have found it is best to put a HDD in level to the ground and not vertical in PC's

Third connect the SATA connections for the Power and the Motherboard, hopefully the new drive that you bought came with a SATA data cable in the box, plug that up to the HDD and then run it to the free Motherboard SATA connection

Once that is complete you have installed your new drive, boot your PC, find disk management by right clicking Computer in your start menu and going to manage, then in that windows you will see the selection that says disk management, find the drive that is not initialized and initialize it, after that it will format itself most likely and voila you have a new drive that you can start saving items and installing programs on