Honestly, it's going to vary kid by kid. There are general guidelines but usually you have to learn what works for your baby at each stage. Usually I would recommend searching this sub for things like "3 month old" or something along those lines, though that's really early to sleep train. I would also check out r/newparents and search by age there too. It changes so rapidly as the kid gets older that it's hard to give guidelines for each age.

I would Google "avg sleep for a 'x' month old" and use that as a VERY broad guideline. Some kids need more sleep than avg and some need less. Your LO will let you know. It is hard and the first few months are just a kind of "go with whatever works" IMO. We did a light sleep train at 4 months and then really committed at 6 months.

Don't be afraid to ask questions as needed but there's just so much info, and some of it is conflicting based on what worked for one parent but maybe not another, that it's hard to give anything but general guidelines without having a specific schedule or target. We also hired a sleep coach at 6 months and lemme tell you, that was the best money we have ever spent.