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 some<em>thing</em>, 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.