I will like to know the reasons behind it and try to help myself

Not my pay grade, not my wheelhouse, not my circus, not my monkeys, not my problem. If I like the job and pay I stay. Otherwise I go.

It's good to here about the employment but what kind of job s is that

I’m offering online employment only

I would look at when did they start working ., education .. any reason ? .. there must be a reason .. comparison may not be completely right .. if... this bothers me I would inquire from HR to understand why .. when being employed maybe you friend had better negotiated but you accepted the offer .. if you must, ask without fights .. if not happy look for another job and resign.,
Another way on this is to wait for you best increment because you work excellently and this will be noticed . more

I would look at when did they start working ., education .. any reason ? .. there must be a reason .. comparison may not be completely right .. if... this bothers me I would inquire from HR to understand why .. when being employed maybe you friend had better negotiated but you accepted the offer .. if you must, ask without fights .. if not happy look for another job and resign.,
Another way on this is to wait for you best increment because you work excellently and this will be noticed . more

Start looking for a new job immediately. Once you have a prospect you can live with if needed, then you ask your current employer for a raise or... promotion. You can't threaten to leave if you're not prepared to carry it out, they will call your bluff. You don't have options if you don't have anywhere to go. Some employers might fire you immediately or begin "documenting" your failures to build a file that justifies your firing. You don't want to work for them! Always have a backup plan! more

I would usually ask for a raise first before looking for a new job, but it depends on the circumstances.

Why ask first?

The pay difference may have... a legitimate explanation (more experience, specialized skills, longer tenure, different qualifications, or performance history).
If your employer values you, they may correct the gap once it is brought to their attention.
Staying can be less disruptive than changing jobs if you otherwise enjoy the role, team, and career opportunities.

When I would start looking elsewhere:

If the company refuses to discuss compensation transparently.
If there is a pattern of undervaluing employees.
If the pay gap appears unfair and there is no clear path to correcting it.
If market salaries suggest you're significantly underpaid beyond this one comparison.

A practical approach is to do both:

Gather evidence of your contributions, performance, and market value.
Request a compensation review.
While waiting for the outcome, quietly explore other opportuni more

I wouldn't because I am not in competition, I am a person believes that I I deserve I must get without fighting for it. I have been in this scenario... before where my junior got more than me just because my superior wanted to frustrate me so that I resign, but I didn't  more

Je ne me préoccupe jamais de l'assiette d'un autre. Je suis indépendant.

I would confront management and give them a chance to properly compensate (past and present) and or explain the gap. Short of this I’d begin seeking... another job. more

I worked at the New York Times as an Art Director. Another art director told me that he ask for a raise from the design director. He received the pay... increase and probably is still working to day. Later that month I started thinking about my time and experience and worked up the courage to ask my design director for a pay raise. He refused to increase my salary. He continued to look for reasons to move out of my section. Later that year he offered me a buyout and told me that there wasn't any jobs for me to move within the company. He didn't like me. And made it his mission to remove me. This is a strategy business do when they don't have any more favor for you. So maybe I should have looked for another job. Because losing this employment is an ugly view off how businesses move when you are not their priority.  more