Ok, i created a account for some1 for webhosting since im a reseller, and i was testing his account and when i looged into WHM under his username/pass i was able to change everyones stuff, why!!!???

That's something that would be better sorted out with your host directly. You should contact them, and let them know of the problem. As a reseller, there is probably little that you can do to fix a problem like that. However, maybe you should try to delete, then re-install the account.

You have a reseller account able to create other resellers I guess, it must be like that if you can log into whm with clients username and password.

In that case in your WHM you need to go to Reseller Center, select your client and edit his/her privileges.

If you chose a good host, they should have a good support team who would be happy to help you with this.

As suggested, if you are a reseller, you probably will not have access to reseller center, and should contact your host.

Agreeing with everyone. If you are a "shared" reseller (not VPS or such) only a couple of hosts allow you to resell accounts with their own WHM (VERY rare).
Generally as a reseller you should only be able to create accounts with cPanel, as suggest contact your support for details on how they have you set up...

Did you give the account reseller priveleges? If so, make sure to edit their reseller priveleges in the Reseller Center and remove the priveleges that you don't want them to have. Especially, All Features.

Yes, your host must have given you Full Access, which should not have been done under any circumstances by the way, and then you gave him Full Access to the server unintentionally. This would be something you should take up with your host as soon as possible, because if this person realizes this, then he will in turn be able to give people full access to the server. This will be a major security flaw in the shared server you are on, because with full access comes full access to root and SSH, this means you and the people you create accounts for will be able to delete and modify any of the files on the server, including the operating system. This is very bad.