"Please check my sentences" or "Please check these sentences". It's even better in a question: "Could you please check my sentences?" "Next winter will be cold, so we'll use our stove." It's easiest to keep it all in the same tense. "Are using" is possible for the future, but it isn't expressed well in your sentence. "After the water in the kettle had boiled, I prepared tea." Note past perfect and past simple here. "I have broken knees from my bicycle accident." This needed a lot of rewriting. Remember that "a" means "one", so you can't use it with "knees". Also, "fall down" is not exactly right. You would say "my fall from my bicycle", but "my bicycle accident" is most natural.