If one was to take online classes their senior year, should they add it to the Education section of the common app where it asks for current or recent year courses?
Yes
What type of online classes?
If you high school education is being delivered on-line, then yes, this goes in the Education section.
If you’re you’re just taking a Coursera or similar on-line class, no, that’s an activity.
Like AP Bio or AP Stats
“Type” of classes, per the examples provide, not specific course titles.
If these were delivered through your high school, or another accredited source, then yes.