I can't find them anywhere.. I downloaded all the missions and the sword, but where do I find them to play? Do I have to be connected online to play them?
If you're referring it the Benedict Arnold missions they become available when you get to New York which if memory serves is right around sequence nine, however narratively, they fit most elegantly into the plot right after sequence eleven so I would wait until then to initiate them otherwise Connor's attitude toward George Washington won't make much sense.
I think they're in New York based on the character bio of that Benjamin Tallmadge.
"I'm a teenage assassin executing some fun." - St. Jimmy
Please feed the trolls, it's hilarious!
How about the Maya mission?
The Mayan Ruins mission counts as a "Captain Kidd treasure" so you should have access to it as soon as you can take the Aquila out which I think is sequence seven.