Here's how the money is being used (somewhat vague).

"Microsoft plans to lend $225 million at subsidized rates to preserve and build middle-income housing in six cities near its Redmond headquarters. It will put an additional $250 million into low-income housing across the region...the remaining $25 million will be grants to local organizations that work with the homeless, including legal aid for people fighting eviction."

Here's the projected impact (also somewhat vague).

"The Seattle Times reported Wednesday that if the $500 million were put into one project, it would create only about 1,000 units, so instead Microsoft will most likely put smaller amounts in many projects to help build “tens of thousands of units.”

Here's the need: "Seattle region needs 156,000 more affordable housing units [today].and will need 88,000 more by 2040 if the region’s growth continues."