@ImNotBella Honestly, it's the best thing you can do to help. StreetLink are total heroes.
If you ever see a rough sleeper and you feel safe talking to them, it can be quite nice to buy them a hot drink (ask them first what they want, as some have very specific tastes, and it's about preserving dignity) and have a chat. Don't give them any personal details about you and don't make any promises - it gives them false hope. But do have a chat together and do log them with StreetLink.
There are lots of homeless charities. A couple of national ones are Crisis and Shelter. If you want to donate money or time, you're best placed going via a charity than trying to help a rough sleeper directly - that way, the people who do have specialist training are freed up to support the rough sleepers instead.
And of course, you can help with lobbying. I have a vague recollection that you can only post links to petitions on a specific board on MN, but if you look up Shelter's website, you can find loads of campaigns you can support without spending any money.
Homelessness is hugely complicated. Some people are from naice middle-class families and have ended up on the streets due to a relationship breakdown, and if they could get the right specialist advice, they could move into funded accommodation. Some have complex mental health issues and don't actually want to leave the streets, and require support delivered to them where they are, as more help can be given to improve the quality of their lives but without moving them into a property.
You can't be expected to understand or assess why someone is on the streets, and what you can do to help - and that's without first spotting who all the scam artists are, because there are some - so the best thing is to throw your support into the people who know how to provide immediate and ongoing help.
Bless you for worrying about this man.