those,these and this 有什麼分別?

this係單數,姐係得1樣野
Example sentence:This is a bag of Mark.
these同those係2個/以上既野
these就係同我地近既可以伸手就拎到既野
Example sentence:These bags are mine.(bags are next to me)
those就係遠既,伸手拎唔到既野,要行過去拎/無辦法拎到既野
Example sentence:Those birds are flying in the sky.