I can see multiple questions being asked in the question title and the details. I will try to answer all of them.

 > What is the main difference between utility and security tokens?

A security token gives you legal ownership rights to the companies, products or platforms where it is used. And SEC decides whether a token is a security token or not. They are the authority. 

For example, if Golem is marked as a security token by SEC, that would mean GNT token holders have ownership rights to the golem network.

Utility tokens do not provide ownership rights to its network participants. For example, ether is a utility token but it doesn't give you ownership rights to the decentralized ethereum network.

>  Since almost every single news is closely connected with SEC approving or ignoring crypto i would like to know a bit more detailed awnser. 

I don't think every news is talking about it but it sure it getting a lot of attention. The main reason is that security tokens provide a lot more legal protection. Coinbase or other exchanges will need regulatory approval before they list security tokens. If they ignore regulation, they will be prosecuted for violations.

>  I do understand most of it but don't know why is it of so high importance for new investors. Thanks ahead.

It is easier to list utility tokens in exchanges than it is to list security tokens. Also, security token traders will most likely come under the same laws that rule other forms of securities. Hence, trading security tokens will make you a lot more binding to regulations then trading utility tokens.