Hi,
Writing a will means a person want to pass on his/her property which he/she owns, to legal heir/heirs after his/her death. The person receiving such property through will has to probate the will after the person's (making the will) death to own the property and in the process has to pay charges in the court. He/she will have to produce documents of the property along with other required documents, which has been given to him/her through will.
In your case, find the property documents through local tahsildar/talathi of the area where the property is located. Every property has its record in the khata maintained by the talathi of the concerned area.
Through will, your mother can distribute her property as she wishes among her legal heirs. In case of absence of a will, all her property will be distributed among all her legal heirs equally.