Yo, things about helping people--one cannot help others that well if they have issues of their own that they haven't mastered control of yet, or anything similar or parallel to 'being able to handle own concerns, maturity and growth'. It's a basic concept being taught in Psychology with regard to aiding other people in the future, especially in the clinical setting, that one's efficiency can be easily hampered by their own concerns in the way
Which, in this context, means that you are NOT USELESS IF YOU FEEL YOU ARE UNABLE TO HELP OTHERS. You have concerns of your own--help yourself
In doing so, in the future, you'll be more able to help others by learning how you deal with these things yourself AND the feelings one may have when under this kind of idea. Other people knowing you're there for them is ok too. "Helping" also means just listening to others. Peer Counseling, as a matter, is listening to others--you can't give advice or suggest ways for them, but you can help by listening to them, giving feedback, etc.
I've seen this being somehow like a trend that people think they're useless because they're unable to "help others". Thing is, people are very well capable of helping themselves; the deed of helping others is helping them help themselves--rather than lead the way, go alongside them. They're searching for a solution, you can be there alongside them; morale support, even if you don't have a solution in mind. They may not seem like they're following your suggestions too--still be there for them.
You can ask yourself why you help others or want to--that can form your basis for later on; self-validation or usefulness should not be the reason on why you want to do so; I recall someone (not from this forum obviously :v) who wanted to help others but when they didn't listen to their suggestions, they became cynical and blamed them instead. They didn't want to feel like a failure but they had issues themselves that they didn't prioritize at the moment or put in mind when they made those reactions.
The point in all this is your motive--you want to return the idea of help; help yourself first, build, develop and bring out your capabilities. Make it a long-term goal for yourself, rather than judging yourself ESPECIALLY if you're between the age of adolescence to young adulthood. What comes to mind, to reference a good show, is Avatar (ATLA), because of the questions Iroh gives--in the time between adolescence and young adulthood, you're in a place where you develop building blocks of knowledge to live by for your future years. To all those who think themselves useless for generally "not being able to help as much as I want to expect it", focus on your growth first. A growing tree cannot provide as much shade as the elders towering above them, but that growing tree can ensure its own health to be able to provide as much in the future.
So just don't judge yourself if you're "unable to help" AND THEN let it upgrade into "I'm useless. Why should I {do this, do that} if {result = inefficient}", or generally termed as rumination.
Maybe you didn't notice at that time, that being there for the other person is also 'helpful'. Rather, what matters.
Tend to yourself. Grow, mature. Focus doing this; you'll be better off later in the future.