I taught myself how to play the piano.我自学弹钢琴。 I'm still practicing on the piano on weekends.每周末我仍旧坚持练习弹钢琴。 I like to cook. 我喜欢下厨。 Both of my parents are good at cooking.我爸妈都很擅长烹饪。 Sometimes I would watch my mom cook and help her cook.有时候我会看着妈妈做饭而且帮助她打下手。

大家翻译的不错

first sentence you write is correct and quite good. so i will translate your next sentence into Chinse line by line. I taught myself how to play the piano. 我自学了弹钢琴。 I'm still practicing on the piano on weekends. 现在我每个周末还在练习钢琴。 I like to cook. Both of my parents are good at cooking. 我很喜欢做饭，我的爸爸妈妈都很擅长做饭。 Sometimes I would watch my mom cook and help her cook. 有时候我会看着我妈妈做饭并且帮她。 glad to help u ,if still don't understand just write some comment to let me know. :D

"我十岁时学过小提琴，学了一年。" would be better. Your second sentence is perfect. "已经**了**年/月/日" means "have/has (NOT had) been doing sth for ** years/months/days". For example, "我在学英语，已经学了1年。" That means "I'm learning English, and I have been learning it for a year." The Chinese for "I taught myself how to play the piano. I'm still practicing on the piano on weekends. I like to cook. Both of my parents are good at cooking. Sometimes I would watch my mom cook and help her cook." is as follows: 我自学过钢琴，现在每个周末还在练习。我喜欢做饭（or 烹饪, which is more formal)。我父母厨艺都很好。我妈妈做饭时，我有时在旁边看，给她帮帮忙。

Hey,karento. You did a great job. This sentence you wrote is right. If you like ,you can delete the “了” in this sentence——我十岁学了小提琴. It will be better I think. The Chinese sentences you want to translate can be translate into these: 我曾自学弹钢琴。现在我仍坚持在周末练习钢琴。我喜欢做菜。我爸妈都擅长做菜。有时我会看妈妈做菜并帮忙做菜。