Grrrr..... Sync questions

Google University isn't helping me and I'm sure this question has been asked a million times. Anything I find on google I'm assuming is from older versions because the options on my zoho don't correspond with any info I've found.

Anyway...

How do I sync Invoice and CRM so that I can add a customer in either or and then either manually sync them or have it auto sync? When I first fired up Invoice it did allow me to import my CRM contacts/profiles however I can't for the life of me figure out how to get it to sync again now that I've added some cutomers in Invoice and some in CRM.

Thanks