and but 可以单独用在一个句子中吗?

当然可以.
如"And(But) secondly I like it."的意思可以是“而再者,我又喜欢它.”

My Weekend
I always have a busy and colourful weekend. On Saturday, I often do my homework. Then, I read some comic books or story books. After lunch, I often clean my room and wash my clothes.Sometimes ,I will draw some pictures when I finish cleaning and washing. After dinner, I often go out to play badmiton with my friends. But sometimes,we also play hide-and-seek together. In the evening, I often watch TV with my parents or play computer games by myself. After that, I am going to wash my face and feet. At last, I go to bed. On Sunday morning, I have to go to English training school to study English. In the afternoon, I often go to bookstore to buy some books. What about you? What's your weekend like? Can you tell me, please?
我的周末 我总是会有一个繁忙但又多彩的的周末. 星期六我通常做我的作业.然后我读一些漫画书或故事书.午饭后我经常打扫我的房间和洗衣服.有时候我也会在我打扫完房间和洗完衣服后画一些画.晚饭后我经常到外面去和我的朋友打羽毛球.但有时候我们也会一起玩捉迷藏.晚上我经常和我的父母一起看电视或自己一个人玩电脑游戏.之后我就去洗脸和脚.最后我才去睡觉. 星期天早上我不得不去英语培训学校学英语.下午我经常去书店买一些书.你呢你的周末是什么样子的请问你能告诉我