Mandarin introduction

Really loving Mandarin so far! This is what I've learned in my first week. :)

你好！我是Brittney。我是十八岁。我是美国人。 我有一个妹妹。 我会说一点中文。我喜欢学中文和韩文。我喜欢喝咖啡和茶。
谢谢！再见！

What you have written are perfect sentences.  You did a great job for your first week.  A suggestion though...

When strung together they are not too natural.  For example, when translated into English, it becomes, "How are you? My name is Brittney.  I am eighteeen. I am Amerian.  I have a younger sister.  I can speak a bit of Chinese.  I love to study Chinese and Korean.  I love to drink coffee and tea."

As you can see, too many I's and all are short simple sentences.  A native speaker would have written something like this, "How are you? I'm Brittney, eighteen years of age, an American.  I have a younger sister and I can speak a bit of Chinese. Chinese and Korean are my favorites to study and my favourite beverages, coffee and tea."  So if you translate this into Chinese, then they will be more natural.  This is just a suggestion to show you to improve faster if you can translate your thoughts this way...

你好！我是Brittney, 今年十八岁, 是个美国人。 我有一个妹妹。 我会说一点点中文。学中文和韩文是我喜欢的功課, 咖啡和茶是我我喜欢的飲料。

Mandarin introduction

Really loving Mandarin so far! This is what I've learned in my first week. :)

你好！我是Brittney。我是今年十八岁。我是美国人。 我有一个妹妹。 我会说一点中文。我喜欢学中文和韩文。我喜欢喝咖啡和茶。
谢谢！再见！

你的中文很棒，几乎没有什么语病

Mandarin introduction

Really loving Mandarin so far! This is what I've learned in my first week. :)

你好！我是Brittney，今年十八岁，是美国人，会说一点儿中文。我喜欢咖啡和茶。我有一个可爱的妹妹。
谢谢！再见！

Mandarin introduction

Really loving Mandarin so far! This is what I've learned in my first week. :)

你好！，我是Brittney。我是今年十八岁。我是美国人。 我有一个妹妹。 我会说一点中文。我喜欢学中文和韩文。我喜欢喝咖啡和茶。 谢谢！再见！