Joshua 17:12, "Yet the children of Manasseh couldn’t drive out the inhabitants of those cities; but the Canaanites would dwell in that land," means that the tribe of Manasseh, despite being allotted territory in Canaan, was unable to completely conquer and remove the Canaanite populations from certain cities within their assigned region. As a result, the Canaanites continued to live alongside the Israelites in those areas.

Here's a breakdown of the meaning:

"Yet the children of Manasseh couldn’t drive out the inhabitants of those cities...": This highlights the failure of the tribe of Manasseh to fully conquer and expel the Canaanite inhabitants from specific cities within their allotted territory. The conquest was not a complete victory, and pockets of resistance remained.
"...but the Canaanites would dwell in that land.": This indicates the consequence of Manasseh's inability to drive out the Canaanites. The Canaanites continued to live in the land alongside the Israelites. This created a situation of co-existence, and potential future conflict.

Implications:

Incomplete Conquest: This verse illustrates that the Israelite conquest of Canaan was not total. It was often selective, focused on strategic areas, or simply less successful in certain regions.
Compromise and Coexistence: The Israelites were forced to coexist with the Canaanites in these areas. This could lead to cultural and religious mixing, which was often warned against in the Old Testament.
Future Problems: The presence of Canaanites within Israelite territory would lead to future religious, political, and social problems, as the Canaanites were not monotheistic, and practiced religions and social systems that went against God's instructions to the Israelites.

In essence, this verse points to a limitation in the Israelites' conquest and sets the stage for future challenges as they try to establish themselves in Canaan. The presence of the Canaanites represents a potential threat to the Israelites' religious purity and national identity.