The thing is that it's a bit different from the previous three games in the series. Instead of leaving for work one hour before it starts, you now leave at the exact moment work begins. So if you begin work at 10:00, your sim can do other stuff right up until 10:00 and still not get in trouble for coming in late.
When the exact time when work begins hits, your sim will automatically leave by going into a car that comes to pick you up. If there is some bug or other thing that prevents this from happening, click on your sim and select "Go to work" to manually trigger the response of going to work. This will prompt your sim to leave for work right away.
For the most part, your sim will leave for work on their own, so you won't really have to worry much about it at all. The only thing is that a lot of people are confused because they are used to leaving early like in the previous games.
You should always try to get to work, because missing work will severly reduce your chances of being promoted, and if it happens frequently, you will get fired (unless you have a perk to prevent that from happening).
How to leave for work in The Sims 4: Get To Work expansion packLeaving for work in The Sims 4: Get To Work is just the same as in the regular game; basically just wait until the exact moment the work begins, and your sim will be picked up by a car outside the front door.
When your sim leave for work, you will be asked if you want to tag along, or stay at home. If you come along you can do all the features that are only found in the The Sims 4: Get To Work expansion pack.