There are two ways you can increase the number of workers you have.

The best way to get more workers if you need them fast is to hire them. If you hire workers, they produce goods for a certain amount of time and then leave the station. You can't see these workers, but you can see that the total number of workers you have has increased after you have hired some.

However, more experienced Klondikers advise you to plan for the future and make long-term investments in your workforce. Provide housing for your workers, and they will stay forever! Just buy tents, cabins, apartments or any other type of residential buildings at the Market. Most buildings can be bought for coins :)