How would a transition to socialism work in practice?

Decade by decade, have more things be run by the government rather than for-profit enterprises.

For example, in the 2020s, the US could transition to a Swiss-style healthcare system. In that kind of system, everybody would have insurance provided by a private company, but the most basic plan would be very cheap and offered by every company, and there were subsidies available so nobody in the country was uninsured, no matter what their financial situation. The US could also have a government owned bank that operated out of every post office that provided extremely basic banking services with zero fees. Private banks would still be able to compete with that, but they'd have to compete on extra services that the government bank didn't offer.

In the 2030s you could tackle education and housing. All state-owned universities could offer education with a $0 tuition and all textbooks available digitally for free. Maybe for some majors you'd have to agree to provide some public service to offset the cost of that education. Like, a doctor might have to agree to serve for 5 years in a remote area that typically doesn't have good medical coverage. Or, a lawyer might have to spend 5 years working as a public defender. For housing, the government could buy and own housing. Any citizen could get an apartment and pay a low monthly rent directly to the government. Subsidize that rent so that if someone couldn't afford to pay any rent, they could still live there. Private homes could still exist, and would be more spacious and more luxurious, but everybody would at least be able to start with something decent.

Then you could tackle transportation. Tax private vehicles and use that to fund public transit. As transit got better, fewer and fewer people would feel the need for the luxury of their own vehicle, but those who did could continue to subsidize public transit for the rest (instead of the current situation where cities subsidize drivers).

Then you could look into food. Maybe everyone gets the equivalent of food stamps. Maybe instead of throwing money at private farmers to grow corn, making corn so cheap that it's almost free, resulting in awful things like high fructose corn syrup in everything, the government could be responsible for some basic crops, and allow private farmers to grow specialty things / luxuries.

Media would be easy -- just set up something like the BBC but for the US. Most other countries in the world have something similar.

Bit by bit, just chip away at all the for-profit things and allow the government to either take it over entirely, or to provide a bare-bones version that was available to everybody, while allowing people to keep running their own private for-profit ones that offer a more luxurious experience for people who want to pay more.