If you've ever seen a dog on a leash suddenly refuse to walk any farther, you know how much resistance one little pet can put up. Resistance means "refusal to comply with or accept something."
An individual person can put up resistance against something she disagrees with or doesn't want to participate in. On a larger scale, groups of people and even whole countries can display resistance, like when the British put up resistance against Napoleon. Another meaning of resistance is "the ability not to be affected by," like a resistance to getting colds, which you can imagine as your immune system putting up a fierce resistance against invading germs.