How do I put brake fluid in the white plastic box mounted under the hood or do I

Thanks I was wondering if I could just unscrew the top of the box and pour some in or is there a place to buy the special funnel. I really don't have any extra money to pay anyone and gas to drive anywhere (other than the 5 miles to school and back) This is sad (as I don't want to further damage my car) but true (I just used the last money in my account for this months insurance) That is where and why this forum came into play. It is the only resort I can come up with in this situation I am currently in. I have found out it is the ABS fluid container that is empty (and the system, currently not working, needs to be replaced as do my rotors and pads as they are quite worn on one side). At this point other than the squeaking noise when I make left hand turns the brakes work good and not giving me any problems stopping. Regardless of any of that, this is what I would be very appreciative knowing CAN I somehow get fluid into this white box for FREE? CAN I just take off the lid/top (2 screws)and do it myself? Does anyone have a funnel I can borrow lol? Or.. Is it a BIG No No for some really good legitimate known reason? If this is so then I will not do it. I'm getting desperate. .. damn...heavy sigh....I would be grateful for more suggestions or information please?