I think people like to complicate things but in my opinion red light therapy at home is very easy.
Get the light device that is appropriate size for the area you want to work on. Handheld panels are very versatile but the best bunk for the buck you get from table top panels like Mito PRO 300X for instance.
Place the light in 6-12" away from the area you want to treat and start the session. If you do light therapy for skin - that does not require very strong intensity of light - 5-10min is all you need per area. If you treat muscle-joints-organs the light needs to penetrate deeper into tissue, so you need stronger light and longer session. Keep light no further than 6" away and set timer for 10min. It's that easy.
If you just start light therapy, until your body get's used to this new therapy - perhaps you want do start with shorter sessions 3-5min in the beginning and as you feel comfortable and your body tolerates well the light therapy - you can do longer sessions 10-15min per area.
You can do session every day or every other day - to give your body time to process the effects of red light therapy on your skin and tissues.
Remember - this post is NOT a professional advice so if you have any problems you want to treat with red light therapy - always refer to the relevant professional specialist (physiotherapist for instance if you treat your achy joints or muscles)