i don't take concerta specifically but i do take ritalin LA which has the same active ingredient (methylphenidate) and lasts roughly the same amount of time. obviously i can't give an exact profile of what concerta is like since they have different concentrations and release mechanisms and stuff but my experience with ritalin has been much better than my experiences with other adhd meds i've taken (adderall and vyvanse). it's kind of tough to tell if it's working when i'm taking it but i stopped taking it for a few days and definitely noticed the difference.
the main side effect in my experience is jitteriness, this is considered less severe with methylphenidate compared to amphetamines and will likely go away within a week or two. some people report experiencing nausea (with both ritalin and concerta) but i haven't experienced it.
if you're sensitive to medications/stimulants, you'll likely have a better experience with methylphenidate than other adhd stimulants. if the jitteriness is too much i would recommend a non-stimulant such as strattera or intuniv.
with concerta some people report a "zombie effect", which entails feeling like you're on auto-pilot all the time and being disconnected from your emotions. i had this on adderall, if this isn't a dealbreaker for you and the benefits outweigh the drawbacks then feel free to keep taking it, i took adderall for 3 years despite this and it worked nicely.
however, if you experience this effect and it IS a dealbreaker, you can stop taking it at any time. lots of people have medication holidays where they stop taking their meds for a while. i did this with adderall (didn't take it on weekends or over the summer) and i did this a few days ago with ritalin when i noticed i was experiencing symptoms of mania.
on the topic of mania!!!! since adhd meds typically increase dopamine, they can in rare cases cause mania or manic symptoms. this is more common when taking multiple medications at once, for instance i was on both prozac and ritalin when this happened to me. it was pretty easily resolved but make sure to stop taking it for a bit if you experience symptoms such as restlessness, uncharacteristically dangerous behavior, less sleep than usual without feeling tired, and extremely elevated mood all at once. elevated mood is very common with adhd meds and this alone is not a sign of mania, just the medication working as usual.
all in all, don't stress too much about it, you'll likely benefit from it and if you don't it's nothing to worry about, just stop taking it and talk to your doctor about how it didn't work for you. everyone is affected differently by given medications. signs that it's working for you include quieter mind (you'll know what this means if you experience it), improved focus on one thing at a time, improved motivation to do things, and more. the length of this post is an example of a benefit, i was able to focus on this for like 30 minutes and go into depth about stuff due to awesome methylphenidate powers ❤️
tldr: while i don't have much experience with concerta in particular, i would recommend taking it and if you don't like it you can just stop taking it. typically helps with focus, mood regulation, and motivation. common side effects are jitteriness, dry mouth, irritability, constipation, and nausea.
oh and avoid caffeine!!! makes jitteriness and irritability worse.