Starters are generally needed when you use liquid yeast, they lose cell counts as they age and unless you get it super fresh, they don’t have a high enough cell count for most beers. The other downside is liquid needs to be aerated.
That’s why when your starting out brewing beer, dry yeast is the best option. It has a consistently high cell counts and can tolerate low oxygen levels in the wort. Sometimes it can get frustrating if the first couple of batches turn out bad and it can cause a new brewer to give up. Brewing good beers right away can help you gain more confidence. Eventually you can try your hand at liquid yeast, all-grain, lagers, etc.
Measuring the starting and finishing gravity can help troubleshoot problems. Keeping notes during the brewing process will help as well.