Charmed Season 1
Charmed Season 2
Charmed Season 3
Charmed Season 4
Charmed Season 5
The sixth season opens with the sisters traveling to a mystical island to save Leo. After he returns he decides to stay on earth until he figures out who sent him away making life hard for Piper who is trying to adjust to her role a single mother to Wyatt. Leo is extremely suspicious of Chris, who has become the sister's new Whitelighter, and whom they have grown to trust. Most of the season deals with his reason for traveling back in time and his true connection to the Halliwells.
Phoebe gains the power of empathy allowing her to feel the emotions of others, and with this ability she can tap into the powers of other magical beings. Her relationship with Jason becomes more serious as they decide to live together.
Paige begins taking temp jobs to create a life separate from magic but finds this difficult when each job leaves her in a supernatural situation. Through this she meets Richard Montana, a witch who has given up using his powers.
Magic School is also introduced as a place where the future generation witches, Whitelighters, etc. are trained in their powers and it becomes a permanent location for the sisters to go for protection and information. Here they meet Gideon, the headteacher, a Whitelighter and an old friend of Leo's. As the season progresses it becomes clear that Gideon has become twisted in his belief of protecting the 'greater good' and in doing some unknowingly changes the future drastically.
Another 2 seasons (Season 7 and Season 8) but let me finish Season 7 first :-D