I am running the QT bitcoin-core on my home PC for a week... I was told that I need to allow outbound connections, otherwise it is not a full node.
I see the standard 8 connections, thus I guess I'm not contributing. My question is: how do I allow outbound connections?
You're misunderstanding things.
A full node is one that has
all the blocks. By using bitcoin-core you always have
all the blocks, thus you're always a
full node.
Outbound connections are allowed by default in most circumstances. Bitcoin-core makes 8
outgoing connections. You do not contribute to the network unless you allow
incoming connections. You can allow incoming connections by
forwarding your ports, but that's done automatically for you by UPnP, unless you have an old router or disabled it.