SQL report 'Disk Usage by Tables' Data and Indexes

In the SQL report 'Disk Usage by Tables', there are two columns, data and Indexes.
Does the number on Indexes column decrease after rebuilding index?

When I searched online about rebuilding index, for SQL 2008 standard, indexing is 'offline'. Does it mean that, if I want to schedule rebuilding index, I have to schedule to take database offline before indexing or will be done as a part of the maintenance plan for rebuilding index?

When I ran rebuilding index in the past, I didn't have to schedule to take offline the database, but applications can't access database. I wonder if it's just ok to schedule a maintenance plan without talking database offline first.

Also, when I test reorganizing index, to end users, it's the same effect, applications can't access database. But articles in internet say, reorganizing index is 'online' operation. I wonder what's the  difference to the view of end users if both operation makes database hung.