There are multiple layers in this shutdown:
1. This is a "partial government shutdown", so only some agencies (homeland security, state, SEC, etc) are affected. Some agencies like the Department of Defense are not affected and funded at previous levels.
And
2. There are different levels of "federal workers":
- "Essential" employees: government workers whose job are deemed to endanger "life" or "property", so they are working without pay and told to report to work. These people will (very likely receive back pay once the shutdown ends)
- "Nonessential" government employees: people who are not currently working and not receiving paychecks. These people will also most likely receive backpay once the shutdown ends.
- Federal contractors: janitors, drivers, caterers, temporary staff, part time staff, paid interns, etc are not currently working and will most likely not receive backpay once the shutdown ends.
Note that with very few exceptions (like congressmen/congresswomen/senators, etc) most people in the federal government who are affected by the shutdown are not getting paid currently at all, even if they are told to show up to work.