spinach is which contains a lot of calcium is a very healthy vegetable.

--Spinach is a very healthy vegetable which contains a lot of calcium.--

-o-

--Spinach is a very healthy vegetable that contains a lot of calcium.

mum gave which it me good a nice coup of tea

--Mom gave me a drink which is a nice cup of tea.--

sally is who trying to prove her fitness going an excessise programs

--Sally, who is trying to prove her fitness, is going through an excercise program.--

I often spend my summer holidays when my parents were born there in Canada

 
--I often spend my summer holidays in Canada where my parents were born.

OK, here's a hint...

A relative clause is a clause which tells us more about something in the sentence.  The keyword is something, so in your examples, the relative clause can't follow "is" or "gave". Also, think again about the last sentence - the clause doesn't start with "when".

Could you try again, please? :) Also, pay attention to spelling, capital letters and punctuation.