Crispr methodologies, while useful and very simple of use by the initiated, are still very complex. Do you have any experience in synthetic biology? Do you know the different elements present in a gene that determines the intensity and conditions in which it is expressed? What do you know about the genetic code, codon optimization, primer design, cloning and expression vectors, the structure of the CRISPR-Cas9 complex? These are not random words, they are all concepts that you'll need to fully master before successfully transfecting a mammalian cell, let alone your own.
To get a gene you'd like, you'll first have to find its sequence in a gene database, which is very easy and freely available online as well as a suitable promoter, paste these two elements together as well as PCR primers (with restriction sites for digestion by restriction enzymes), and send this to a custom DNA synthesis company. There's a bunch of them, some are way cheaper than other.
Otherwise, you could only buy the promoter strand and get your gene of interest by PCR from a natural source or buy the gene directly if it's a common one such as the luciferase system (but why would you want to glow in the dark lol)
Then you can insert this into a CRISPR plasmid as well as an appropriate guide strand to target a specific location in the genome.
You can lookup the youtube channel "the thought emporium" which did such an experiment on himself but PLEASE research your project for AT LEAST A FEW YEARS before going through with it