Complex sentence: AMD does not distribute Radeon cards directly to consumers (though it did at one time), instead, it sells Radeon GPUs to third-party manufacturers, who build and sell the Radeon-based video cards to the OEM and retail channels.
Split into simpler sentences: AMD does not distribute Radeon cards directly to consumers (though it did at one time). Instead, it sells Radeon GPUs to third-party manufacturers, who build and sell the Radeon-based video cards to the OEM and retail channels.