@DonnaLanclos Absolutely. If you can see a toot from someone you wanna follow, just click the person-shaped icon.
Otherwise, search for the person with their handle and instance (frex you are @DonnaLanclos) and add them.
Complication: some servers shun other servers. I've yet to have this be a problem though.
@DonnaLanclos if they have a consistent handle you can try searching it? yeah, what Ruth said
@DonnaLanclos @dsalo not necessarily if you know their name, e.g. you can search for dsalo and the interface should show all the dsalo people.