Hey, I have experience with the NHS if you want to chat.
Is there a particular area you want to know more about, have you started any treatment so far?
With regards to mental health, the NHS uses a stepped system, with four steps which represent different "intensities" of care. Step one is primary care, which will be your GP, who you should talk to if you're having suicidal thoughts, thoughts about self harm, or generally struggling with your mental health.
The GP will likely prescribe you a first line anti-depressant, something like sertraline, which may help.
You can also either have the GP, or self refer yourself, to step two which are IAPT services; these services are essentially short course therapies like CBT where you'll normally have between five and ten sessions. Unfortunately waiting times to see someone are likely to be a couple of months.
Depending on severity, how things progress etc. you may find yourself also referred to a local mental health team (LMHT) which is step three on the rung. With an LMHT your options are broader, you will have access to things like a community psychiatric nurse, psychologists, and psychiatrists to manage more "off-label" drugs.
Finally, and likely only after being with a crisis service, and once all options are exhausted, will you find yourself at step four which are designated for severe and treatment resistant depression.
That kinda summarises the step approach, hopefully it helps in some way.
Of course different people may enter the model at different points, and this doesn't touch upon things like crisis teams, or the nitty gritty about what might happen if you end up in hospital in a crisis etc. but I'm happy to also talk about that if you want to know more.
If I may also suggest you talk to the folk in the Recovery Discussion forum, as you may find they have better experiences with navigating the health system and, excuse the pun, coming out the other side.