a union is a legally protected way for works to collectively bargain with their employers. Internally, union dues are used to pay for legal assistance (among other things) that can help the workers. A union can make the affiliated company do things by creating legal agreements and organizing strikes. A company often finds it is easier to give into a unions demands rather than have their employees stop working and hold signs outside letting everyone know that they are being treated poorly. A company can tell a union to fuck off and they often do, this leads to the workers going on strike and bringing business to a standstill.
Almost every right that workers have today has been won by unions, sometimes violently. 40 hour work weeks, weekends off, vacation days, sick days, health benefits, minimum wage, overtime pay, and many others are all from the collective bargaining power of workers unions.
Worked as a computer repair tech forever ago. We ended up with tons of spare parts and abandoned computers. I took a few home and looked for things I could use them for. Quickly found Linux and gave it a shot. It was perfect, I didn’t need to spend $100+ for a copy, there were tons of options, and I could do anything with it. Spent the next 20 years using it on every computer except my main desktop because of games. At one point I was 100% Linux and all I played was WoW using WINE. Now I’m back to 100% Linux thanks to steam and proton making a healthy chunk of my library playable.
Any time someone comes to me with an old computer my recommendation is to throw Linux on it and get a few more years of usefulness out of it.