All aliens need herbs to heal themselves after battles or a fall down the space-stairs. Cultivating herbs is a very easy task that can earn you a few credits quickly on the marketplace, and it's also much cheaper to pick your own herbs instead of purchasing them from other aliens.
To begin your horticulturalist career, head to the General Store on Georgetown's Market Street to buy seeds. All aliens are born with innate knowledge on green and blue herb cultivation, so just grab a few seeds for those. As you become a more experienced herb farmer, your knowledge in Horticulture will increase and you'll be able to handle growing the more powerful herbs which would eat the face off a newbie.
If you're ready to plant your seeds, just stroll on over to KaldaBerth Gardens in Georgetown's Industry Place. Click on the seed bag image, which pops up a selection box where you can choose which herb you wish to plant. Once you've made your choice, click on a square of your garden plot to plant that herb. Each herb you plant costs 1 motivation.
Every herb takes a different amount of time to grow. The more potent the herb, the longer its growth time. After herbs have grown the unsightly pile of dirt you made while planting them will be replaced with a beautiful herb, unless you're growing Obsidian herbs, in which case the unsightly dirt pile will be replaced by an unsightly black mess of an herb which is leaking some weird gunk onto the garden floor.
Once the herbs have grown, you can pick them. Picking takes 1 motivation per herb bud, but that gets you a lot of herbs each time you do it. As your knowledge in Horticulture increases, you get more herbs from each bud.