I guess it depends a lot on their symptoms, and if a lot of symptoms are caused by swelling around a brain tumour, then things like steroid medication or radiotherapy to reduce swelling and symptoms can help 👍
If you are referring to what doctors can do to make someone with a brain tumour feel better, I guess it would depend on the location, size and symptoms of the brain tumour. In some cases, doctors are able to operate and remove the brain tumour. In other cases, this is not possible, so all they can do is make sure that the patient is not in pain and is as comfortable as possible. As Nuru said, steroid medication or radiotherapy can help with the associated symptoms.
I don’t work in that area of medicine but the answer to your question is probably far-reaching… There is feeling better in the medical sense (so medicine or surgery or whatever the doctors feel are appropriate options) and also feeling better in the emotional sense. I think its important to remember the emotional and psychological stress of being ill.
Like others have said, medically helping someone with a brain tumour includes removing the tumour where possible, and using appropriate medications to deal with the physical symptoms. In the long term, people with brain tumours will probably need help with everyday function if there are lasting symptoms – which can be with vision, walking or using hands, poor memory and attention, and emotional difficulties. Any remaining difficulties after the appropriate medical help should be assessed as soon as possible, and be referred to a neurorehabilitation specialist or other appropriate long-term care service. In the short-term however – anyone can make anyone else feel better by listening empathetically, helping them engage in something fun and meaningful, and having a good laugh together 🙂