Terriex. I know this much be all very worrying and confusing. How bad, or not this is depends on so many things. The scoring they use to determine how slow, or fast growing they think the cancer is, whether it is still located inside the prostate, whether it has spread outside the prostate into the surrounding area or not, and if it has spread somewhere else.
Obviously it's much better to have a slow growing one, contained within the prostate, but all of these things take time to work out. How many tests has your dad had, and are there more to come. Has a treatment plan been worked out yet. I understand you might not want to put personal details on a forum like this.
You mention lymph nodes being 'slightly raised", I assume you mean enlarged? There are many reasons for lymph nodes to be enlarged, one of which can be that the cancer has spread there, but it can be a sign of infection.
Does your Dad have access to the specialist nurses at the hospital he's attending? They are wonderful at explaining what's going on, and if you are able to go with him to appointments they can explain it to you. If not, maybe your Dad can give them permission to speak to you. It's a complicated illness with all the variations there can be, but knowing as much as you can about it help you to manage your concerns.
Please come back on here though, there are many good people who would help you to understand it, and hopefully ease your worries a little bit.