If you talk about what is needed for obtain dragon, you need go see Poe, the blacksmith. You see the option only if you reach 10k $, else it's invisible. Same for option to increase the space in the barn at 2k.
If you talk about the "classic money". You need sell monsters. You can see the offer in "orderboards" with what thay want, "race and levels" , icon top right. It's a bit difficult at start, i know because you not have all monster yet, but try fullfill maximum of offers quickly, then with time you won't miss any more. You can find interesting monsters in Talia Shop, so it can help, or for catch good skills and integrate later to yours monsters.
When you advance a little in the quest, you can win some money by help some people like "tavern" or "grow vegetables" with Rika, but it's not very efficient. It's more usefull focus on breeding monsters and fuse skills.