Hi Suzanne
Tous is pronounced differently whether it is an adjective ((too) or a pronoun (toos) but this might be better highlighted with examples. -
1. Tous -you don't pronounce the 's' - 'too'
Tous mes copains = All my friends
Tous les pays du monde = All the countries in the world
Tous les garçons et les filles de mon âge = All the boys and girls of my age
( beautiful song from Françoise Hardy!)
2. Tous - the 's' is pronounced - 'toos'
Bonjour à tous! = Hello everyone!
Ils sont tous gentils = They are all nice
Tous ensemble! = All together!
Hope this clarifies matters a bit...