here's how it works.
you own a bakery and make bread.
you want shoes.
you go to a shoemaker and ask for a pair of shoes.
the shoe maker knows you make bread and says "give me a loaf of bread and I'll give you shoes.

You consider this and agree. You trade 1 loaf of bread for a pair of new shoes.

a few months later, you need another pair of shoes. you go to the shoe maker and ask for a pair.
This time the shoe maker needs 2 loafs of bread for the shoes.

You have some options here. You might think that the shoes will be worth the 2 loafs, so you could happily give the loafs in return.
Alternatively you can barter. 1 loaf and a sandwich for 2 loafs instead, but it's up to the shoe maker to agree to this.
There is another option though.

You can work for them! You say "I'll help you with your work, and I'll get my shoes in return. Or I could help you and give you bread as well".

By helping out, you not only get what you want but you also help the shoe maker create more shoes that he can trade for other items.