Essentially yes. Tret is Retin A which is the most potent form of Vit A which can be used topically for skincare.
It goes Granactive Retinoid= very very weak potency, you need to divide the % by 10 on your ingredients list to get the actual % of active ingredient (so a retinol cream with 1% retinol on its pot, but which is listed as granactive retinoid on its ingredients list is really 0.10% etc) These are good starter level retinols. Then they move up through retinols to retin-A which is your tret. A starter tret would be something like 0.025%. That's how supercharged it is.
Most high street and high end creams/serums containing "retinol" (as opposed to a granactive) lie at around 0.3% which again, is good for starters.
If you watch some Nadine Baggott videos, she explains it all beautifully and also says we only "need" 5 products.
A cleanser
A moisturizer
An SPF
A vitamin C
A retinol.
The first two can literally be any you like. One goes down the plughole, the other just moisturises. No need to spend £££.
If you want to treat yourself, then serums are where to spend more. (even though one of the best hydrating serums is Superdrug Pure which is £4.99)
You could also add an acid toner, AHAs for ageing, mature skin or BHAs for oily and blemish prone. Your GG is an acid serum.
The Magic Cream has lots of good stuff in it. Lots of hydration - glycerine and peptides, hyaluronic, a tiny bit of vit C (but at the end of the ingredients list and not a particularly "good" form- the best is L-Ascorbic Acid) a bit of lactic acid again.
It depends on what kind of moisturiser you use, but general rule of thumb is thin to thick. So a lotion would have you putting an oil on top. Nivea blue pot (probably the best hydrator you can get) goes weird if you put it on top of some water based serums (most) so an oil would go first to provide a slip for the thicker cream to settle on.