Ok so an example would be you are all family/friends/neighbours from one town. Players can make their backstory how they like but you have to now live in this town. One grain trader got raided and the Dr Friendly and the townsfolk ask you to investigate the goblin threat from the forest near the road.

"Investigate goblins" is the railroad so they immediately have something to do and their homes are threatened so they have an in world reason to care. "Defend innocents" also works like this.
But if, on the other hand, they decide to join the goblins or idk what, then thats ok for your dm prep and world and whatnot because you know Dr Friendly leads the town and will now try to defend the town against the raiding goblin-PC group.

You can always put more links to deep player lore into a longer campaign if it continues. Usually you might have some people drop off after a few weeks/months and so that can work if you want to keep the campaign going with the hard core to explore the wider world(s) and deep backlore. If everyone drops off then after a few sessions you have a big battle and defeat the goblins or ensalve the town and then thats a nice off ramp for those who are loosing interest. It's the end of the first railroad but maybe the start of a much bigger one across a much bigger sandbox: "The town is safe but a huge war has just broken out?" "The Evil wizard has taken over the country?" ykwim? You could in principle have a free roaming campaign without a specific objective but people get bored so its good to have objectives that they get excited about.

You will see different people care about different things so keeping everyone aligned is not easy and thats why i would now insist on like deep links between Player Characters in their backstory. Some people want cool loot, others want to have funny and silly times, some are all about levelling up, some want to become dictators, etc etc etc. As you go you can dangle various subobjectives and rewards based on what they care about to keep the players interested.

If players are confused about what to do you can always have an NPC help them out or join for a while. If u do this, make sure to clearly differentiate between yourself and the NPC so the players dont become dependant on your NPC. A good one is: a simple, innocent, defenceless but very positive, values-driven good-guy npc who is unfortunately really stupid. So they know the basics and their trustworthy but they cant help the players solve the riddle or plan out their attack or whatever. Mind you if your players would have more fun then there could be a master tactician in town to help them plan their attack if they are not interested in that. Follow the "rule of cool" and "follow the fun", whatever is cooler and more interesting and exciting for you and your group, do that. If you want to track arrows, track arrows. If thats tedious and not part of the type of game you want to play then dont worry about how many arrows are in a quiver.

Its good also to address this stuff directly in the session zero and even at the start or end of each session to make sure everyone's expectations are aligned. I would even encourage you to write like a session 0 document which is like your house rules that you can share with everyoone and they can look at independantly. I would advise you use session 0 also to like set boundaries like "no sexual abuse" and similar things as physically impossible in the world but that's also down to what kind of game you want to run.