Stardew Valley will often throw you a new quest that will net you some pretty coins. These can be through the town bulletin board or by request in a letter to your mailbox. The quests can always be found in your journal if you get lost or forget what you were supposed to be doing.
One of the first quests you’ll be asked to do is to find Robin’s lost axe. She notes that she lost it while out in the woods south of Marnie’s Ranch and that’s exactly where you have to go.
Head to where the mouse is hovering in Cinsdersap Forest above. What you’re looking for is east of where the spring onions grow in that area. You’ll find the axe just chilling as east as you can go before you hit a wall, past some trees.
Pick it up and go give it back to Robin. Note that if she’s in her shop, you’ll need to talk to her behind the counter to gift her the axe. And that’s mission complete for you. Go back into your journal and collect the reward for Robin’s Lost Axe.