Most college faculty can tell you how important grants are but in K-12 teachers are not pushed enough to get them. I believe this stems from the fact that they have not been trained to write grants (it is hard), they do not know where to get them, and it is not part of their annual reviews for salary increase. So why are grants important in k-12? Where does one get them? What kinds of grants are out there?
Grants are important in K-12 because they can bring extra money into the classroom and district. Depending on the grant, this could be money for technology, materials, support staff and much more. Why else is this important? Well when you write a grant, your school gets a % of the money. So if you are in a district that is hurting for money (pretty much all K-12) you are seen as an asset who has brought in extra money which might help to keep your (and others) job. I mean who are they going to fire, the teacher that brought in 2 million dollars or the one who hasnt? Bringing in that kind of money pretty much guarantees your job.
Where does one get grants? You can get them from government agencies such as the NSF and NIH and private businesses. There are tons out there. Sometimes you can search google. Sometimes you need to go to a companies website to find it. But they are out there.
What kinds of grants are out there? Every subject has them. However, there are more for the STEM subjects. So if you are not a STEM teacher I encourage you to look into incorporating technology into your classroom then you can apply for the tech grants. That can help the art or social studies teacher get big $$$ that is offered to the science, math, and tech teachers.
Look, its hard to write a grant. Some can be very long (but remember there are also small grants too). Usually it takes more than one person so you may need several teachers and your superiors to help you. But its worth it. Its worth it to try. Once you write one, even if its rejected, you can use that as a template and eventually you will get one. So good luck!