Here's how it works when you make a roll: The player to volunteer first or think of the plan to overcome the obstacle must make the roll. It's okay if you don't have the highest ability in the group or don't even have the skill! The highest-skilled mouse is not supposed to dominate those skills. Everybody needs practice.
A good description can go a long way towards earning rewards at the end of the session. Always keep in mind your Beliefs, Goals and Instincts when roleplaying a description.
Now, here's how the roll itself works. If you have the relevant skill, roll as many d6s as your skill's rating. Every result of 4 or better is a Success. Any result of 3 or lower is a Snake—it doesn't count. In this case, if you get at least six successes, you succeed. If you get fewer, you fail, and must deal with a twist or a condition. Coward dice!
If You Don't Have the Relevant Skill:
You can act with your Nature skill instead, but if the task isn't related to the four aspects of Mouse Nature (foraging, escaping, hiding, climbing), you run the chance of taxing your Nature skill, which isn't good. That said, your Nature skill is likely quite high, so it might be worth the risk!
Alternatively, there's Beginner's Luck (which is what lets you actually learn new skills). This means you use your Will (for mental tests) or Health (for physical ones). In this case, you can choose either depending on how you roleplay it.
When using Beginner's Luck, the total dice you get to roll (counting teamwork, wises, gear, etc) is halved. So why use it when you can use Nature? Well, Beginner's Luck lets you start learning to use that skill!
Ways to Boost Your Roll:
Keep an eye on your Wises when making tests. If you think a Wise applies to the roll, you can use it to aid a friend making the roll, adding +1d6 to the roll (you can't use a Wise in this way to help yourself). I can nix this if I think the connection is weak. There are other ways to use Wises, but we'll get to those later.
If you have a piece of gear or equipment that you want to use, it might also grant a +1d6 advantage. This can also apply in a more abstract sense—for instance, using some damning evidence you learned could be a "tool" in an argument. Again, it's the GM's call whether or not it helps.
You can use Teamwork. To do this, you must describe how you are helping the main mouse (and they must not decline your aid). This allows you to donate +1d6 to the roll. This is called a helping die. However, you must use a skill or wise that is relevant to the activity. It need not be the same skill, but it must be related (for instance, you can help a friend use Armorer to make armor out of a beetle carapace, but you must use a skill like Insectrist or Scientist).
You can't aid with both a Wise and Teamwork. Also, if you provide a helping die, you are bound by the results just as the mouse you're helping is. You Reap What You Sow.
Only two mice can help at once during a conflict, and I can similarly limit it at other times.
Fate Points and Persona Points
You start out with one Fate Point and one Persona Point, and earn more at the end of a session by acting your Belief, using your Instinct and achieving your Goal.
Fate Points are spent after a roll in which some of your dice came up 6s. If you choose to spend a Fate Point, you get to roll bonus dice equal to the 6s you rolled. So if you rolled two sixes, you get to roll 2d6 more and potentially increase your total successes. Those new d6s are also exploding, so if you keep rolling 6s, you get to keep rolling more.
Persona Points can be used to add +1D to your roll per point spent. You can also spend one point to Tap Your Nature.
Tapping Your Nature
Note that tapping your nature and acting with your nature are two very different things.
Tapping Nature means you get to add your Nature ability rating to any skill or test (adding those dice to the roll). However, if this test is not within Mouse Nature, your Nature will be temporarily reduced by 1 afterwards. If the test is failed, the Nature gets taxed regardless.