Sap is a very useful resource in Grounded, because you will need it to create some early healing items to help keep your character alive! It's also used to create some other important tools and furniture that are pretty much required for getting to the later stages of the game!
To get Sap in Grounded, you will need to locate a stick or piece of wood. While the area you are in is mostly grass and dry grass, you will occasionally come across some sticks and twigs. Once you do, check all around them, because globs of sap can usually be found on stuck on all sides!
Make sure to check the entire length of the wood piece because multiple sap can spawn on them! If you're very early in the game and completing quests, one of these sticks can be found near the Mite cave that the electrical wire runs through that you need to find! You will want to grab some because it gets very dark in the cave and sap can be used to create yourself a torch.
If you need a whole lot of sap, then you can head over to the big Oak tree (red leaves). It's a dangerous spot due to the spiders, but there's a ton of sap to collect in the area. You can also break crystallized sap and it will drop a whole bunch you can get!
Sap is used in a variety of recipes, some of these are Fiber Bandage, Torch, Eyepatch, Armor Glue, Plant Lamp, Workbench, Sconce, and some others that you will unlock down the road!