A monk is a person who practices religious asceticism, living either in solitude or among other monks. A monk can either devote his life completely to other beings or lives his life through prayer and contemplation, but lives in mainstream society. A friar is a type of monk who is of the Christian order, who depends on charity for a living. A friar and a monk can be similar, because monks can be like friars who depend on charity for living but since some monks live in the mainstream society, who rely more on praying than actively living in a convent, this is how monks and friars differ.
Hope I helped:P