A diagnosis at last, but no idea what to do next...

My son is 12 and after raising concerns abut his social communications I finally received the diagnosis for him of ASD. There are so many emotions and I just feel a little lost to be honest. 

The paperwork is a multi-agency report from ASDAT using DSM-5, the levels of impairment are stated as Level 1 for both social communication and restricted interests but I'm struggling to find what this means in real terms in order to help him understand the diagnosis. 

Getting the diagnosis was a long process, I was 'fobbed off' for years and his quirks and foibles where attributed to a range of alternative factors. He is in mainstream secondary school and on the middle/ top flightpath of attainment for his age. The lady in pastoral is his best friend, she looks out for him and helps him to regulate and get through the day. At home all the coping of the day tends to overwhelm him and he lashes out generally verbally but on occasion violently, this is part of him and we as a family try and provide him with the space and time to decompress when he gets home. 

Several years ago he was referred to CAMHS due to self harm and suicidal thoughts, they concluded that until an ASD assessment was done they were not able to work with him. This has finally taken place and the above paperwork was issued. He still has very dark thoughts and has a tendency towards negativity but the incidents of self harm are thankfully few and far between.

During his transition to secondary he became obsessed with the idea that he was abnormal, broken and damaged and was given a family support worker to try and help him through the transition period. It was agreed that we would explain to him that he was possibly on the spectrum and that this could explain some of the struggles he was having. This helped him as he felt that maybe he wasn't broken or damaged but that his brain worked differently. 

When he finally received the diagnosis verbally in November 2018 he struggled with not feeling any different to how he had the day before. He reads extensively and has read books and articles on ASD and knows adults and children on the Spectrum and understands that ASD covers a wide spread of abilities and quirks. There are so many 'labels' and 'classifications' in the literature now but I'm struggling to find any guidance on what the diagnosis of ASD with the level 1 impairments means in more child/ teen appropriate language, I hate the term impairments to be honest, and I have a teen with a compulsive need to understand himself who is unsatisfied with a simple 'ASD' diagnosis, any advice or pointers towards guidance would be gratefully received