Weights for sport
Firstly, you should run all this by your doctor and make sure he/she is ok with it. If you have trained in the past then you probably know what to do to work out to build muscle. Use caution and start off with very light workouts and build up slowly to ensure your metabolism is ok and can adapt. Look and a simple activity like walking to build up your overall stamina. When you start to feel your fitness returning then your can start to step it up a bit.
As far as diet goes, don't try to rush things. Listen to your body. As your training and activity start to increase, your appetite should also start to return. Try to get 5 - 7 small meals a day of good quality, wholesome food. Lean meats, whole grains, vegetables, pasta, rice, etc., standard bodybuilding fare, but only eat as much as you feel like, don't force it at this stage.
As far as supplements go, a good quality weight gain formula would be a good start. Our Mass Daytime Protein would be a good choice. Take one serve straight after training, and the other as snack between meals. If you like it in milk, use that, otherwise mix in water.