Upper Canada Land Petitions are a petition (letter) from a settler to the Lieutenant Governor requesting a grant of crown land* prior to 1827. Up to 1826 most settlers were able to petition for free land grants, after 1826 free grants were available only to loyalist or military settlers. All other settlers had to purchase land.
These petitions are indexed by surname with place of application, date of petition and the number of the petition (which you will use to locate the actual petition).
The petitions usually include the name of petitioner, date of petition, and military regiment if applicable. Some might also include a brief synopsis of how they came to petition for land and why they should be granted the land - an autobiography of sorts that might include names of family members, when they arrived in Canada, where they came from, and if they should get special attention (i.e. they're a soldier or loyalist).
Patents were received by settlers who were successful in their quest to obtain a grant of Crown Land through a settlement agreement (i.e. clearing land in a specific time period).
Patents were not received by those who obtained land through a free land grant. Patents were only issued after the settlement agreement was complete which could take years.
Patents are indexed by Township (1795-1850) and by surname (1795-1825). Indexes for 1850 to present day are available at the Ontario Ministry of Natural Resources.
Ontario Land Registry Office Records were created after land had been granted by the government. This includes transfers of land from one person to another (through sale, inheritence, etc.), and deeds.
Township Papers are specific to a piece of land within a specific township and its ownership. To use these records you should know the location of the land that you're researching (lot number, concession number). Once found you can learn who owned this piece of property and when they owned it.