in our chinese culture jude always mean good virtue as the old saying goes"every gentleman has his jade".When we send jude to someone also want to send the good luck, the force of nature to help him/her avoid of bad luck.I see your jude has a wonderful colour,if it is a real one maybe is valuable.I see a "blessing" in your jade donut, it means blessing and may you will always have good luck!

In Chinese “学”usually means study,at school or by yourself, it is a concept with more extensive meanings.such as "学中文”maybe learn it at school maybe study by yourself."学”often used in our oarl language."学习”always means study more formal, usually means learn something at school.or some activities releated with school."念书" have two meaning ,one is study at school, the other is reading books loudly.but we never say "我念书中文”.so if you are no sure of which word is better use "学”maybe help you making less mistake.

可以感受下你打哈欠时的口腔，这时候是气息产生共鸣最好的时候，在这种状态下练习发声，气息会很匀，很满

hi ,lily,my name is Laura.first i want be your friend ,and teach you chinese. Then about you sentences :
你好我叫美丽莎。this one is OK!
我是法国人你呢。if you use a comma between 人and你 it will be better.
我住在perpignan。this one no problem
我是学生和我一十八岁。please change it to two sentences as:我是学生。我十八岁。as i'm a student and i'm eighteen we don't always say together use 和 to put them together. another point for you, we nerver say 一十八岁,we only say 十instead of 一十for oral chinese.but we will say 二十，三十and so on.
在普通话里我们通常只用“我”表示自己，but we have a lot of way say “我”in our dialect . if you don't want see so many "我”in you sentences just leave same of  them out. so your sentences can be say like :你好，我叫美丽莎，是个法国人，你呢？我住在perpignan，是个学生，今年十八岁。
if your want to learn more please contact me. send e-mail to me([email protected])