Basically, my school is apparently having a network 'update' and are telling us to go to keychain access and trust a certificate. This is what they sent us. Exactly what will happen if I do this any? Do you have any recommendations for what I should do?
Trusting a certificate gives the owner of that certificate the ability to limit security warnings when performing some tasks. These tasks include installing new software, and intercepting & proxying secure connections.
Whether you should follow the request to trust the certificate depends on who owns the computer.
See Should I let my child's school have access to my kid's personal laptop? for a related question over on the Information Security site.
If the computer is supplied by the school and the school want you to install their trusted certificate, then you should do so.
If this computer is yours, I would not trust their certificate. Adding an always trusted certificate is significant step and should rarely be needed on a personal device.
Note the sub-options in step 5:
You can choose to trust the certificate only for certain functions. If the certificate is intended to allow locally developed and signed software to run, then only Code Signing should be required. Maybe X.509 Basic Policy also.
I would avoid trusting Secure Sockets Layers (SSL) until it is proven essential. This trust would allow the school to intercept previously secure Internet connections.
You could incrementally trust/distrust parts the certificate until you found the minimum set of trust required.
Personally, I’d say no. This is an intermediate CA (and below that a Root CA). This enables the owner of that CA to man in the middle your connections. There is no reason to accept such a CA unless there is a large volume of internal applications. The general application of a CA like that is for SSL man in the middle boxes that do traffic inspection — often badly configured.