Is this ERP open source free?

HI,
Is this dolibarr free? what kind of limitations are there if its free/

Yes it is free

Limitations are you support yourself or pay a developer/company to set it up/support it for you.

Support for?? does it having bugs etc?

no software is ever bug-free but besides that, there will always be some sort of tweaking or configuration required for your server/setup.

what if I sell to another company, or if I become a partner agent is it still free or have to pay

Dolibarr is free even if you resell it or become a partner agent.

Just there is rules to be partner agent, that you need to be member of Dolibarr fundation : https://wiki.dolibarr.org/index.php/Subscription_amount_Dolibarr_Foundation

This software is free under GNU General Public License 3.0. It is a web-based application, and can therefore be used wherever an internet service is available. Dolibarr aims to offer free open source ERP and CRM features for people with no technical knowledge, by providing a simple solution.