When you are referring to something general that cannot be specified, you have to use was (literally: 'what'), eg:
Es ist nicht alles Gold, was glänzt – All that glitters is not golddeutsches Sprichwort - German proverb
You also use was when you refer back to a whole clause.
Viele Leute finden Eislaufen einfach, was ich nicht verstehen kann. - Many people find ice-skating easy, which I can’t understand.
What do these phrases mean?
Nicht alles was zählt, kann gezählt werden – Not everything that counts, can be countedAlbert Einstein, German scientist and philosopher
Now make two sentences into one using was, eg:
Mein Bruder bekommt alles. Ich will das. > Mein Bruder bekommt alles, was ich will. - My brother gets everything that I want.
Alles was zählt (Everything that matters/counts) is a popular German soap opera - Seifenoper. The story is set in Essen, northern Germany, and the plot revolves around the unscrupulous Steinkamp family and their company 'Steinkamp Sport, Tanz und Wellness'.
Other famous German soap operas are Gute Zeiten, Schlechte Zeiten (Good times, bad times) and Unter Uns (Amongst ourselves).
In 2007, actors from Alles was zählt appeared in character on Unter Uns, which was the first-ever crossover of two soap operas in Germany.