Use there to refer to a physical or abstract place
There is an old truck
Use their to show possession and it is commonly followed by a noun
Their bird can sing a song.
Use Where when describing location,place or such as "at in or to what place"
The dog hospital is where dogs got to help.
And last Use were to describe an even or omething that has already happened or it is on the past,and use was only to the First and third person.
you were late to the picnic.
I was late to the morning class.