Commercial messages - may not actually be spam. It can be messages that you subscribed to, for example, when you made a purchase in an e-shop or when you downloaded an e-book. Such e-mails should contain visible information about the possibility of unsubscribing. Do not mark such messages as spam, but unsubscribe from them. Only if the unsubscription doesn't work, then it makes sense to mark the message as spam.
Ordinary spam - won millions, dead bankers of Nigeria offers of goods, medical supplies, alarm messages... Annoying but not dangerous. Just don't respond and mark such messages as spam.
Phishing is dangerous and aims to get users' login information. They imitate messages from service administrators (for example, bank employees) and try to take advantage of human weaknesses, such as fear, desire to get rich, and others, to manipulate you. They often seem urgent ("if you don't do something, we'll delete your mailbox TOMORROW!"), contain a link to a page for entering a username and password. The login details are then used to attack computers, spread spam, or break into other systems. You should never respond to such messages and immediately report them to faculty administrators or email@example.com. If the message doesn't ask for login details or other sensitive information (such as a bank card number), it's not phishing. It's regular spam.
Spear phishing - a particularly dangerous version of phishing because it is tailored to the organization or even the user. For example, it can use MU graphics or the logo of Masaryk University, and the link can lead to a page very similar to the MU unified login page, or the MU IS login page. Again, it is crucial not to react and report it to the CIT or firstname.lastname@example.org.