Can you please expand on the topic of "learn the marketing side if only by doing it semi-professionally for a client"? I mean, one side of this spectrum is doi

Can you please expand on the topic of "learn the marketing side if only by doing it semi-professionally for a client"? I mean, one side of this spectrum is doing affiliate marketing or direct-sales/MLM. Other point on this spectrum might be for an engineer to go get hired as a social media "manager" (lots of "jobs" like this on Upwork). What possibilities do you have in mind?