Birth to three

I took my son in for his 18 month check up and his doctor recommended birth to three because kids his age need to know 10-15 words and my son only knows 4 on a good day. Has anyone else been through birth to three? Any recommendations on what to do when they are here? Apparently they go to your home? I’m new at this! Any advice or any info on what they do with your child would be nice! TIA