For US and Canada, entry was evisa. They ended that this past January. See https://evisa-to-turkey.com/news/turkey-drops-visa-requirements-for-us-travelers
For others, use the start of the evisa application process (it will tell you in 1 minute whether you need evisa or exempt) at https://www.evisa.gov.tr/en/apply
So, for US and Canadian citizens, walk right in.