I and my sister went to the supermarket together

Today I and my sister have gone to the supermarket together. Big C is one the scene, where happened a serious case. When we was buying goods in the supermarket, my sister suddenly cried out and only speak one sentence that she has lose her wallet that has a mobile phone inside manufactured by Nokia. This is the second time she has been lose the mobile phone. A small flow of tears from the conner of her eyes streamed out but she still tried to keep back her tears. I can see it. I have to admit that the thief's professional skill is very skillful stealing everything. I don't think that his skill can be well up like this. The thief has hiden his face a clever way. He thrust his hands into her pockets while pretending to buy dry beef at the next stall. He took advantage of the situation to merge into the crowd who was going shopping to prepare mechandise for the Tet holiday. Security personnel in the supermarket warned customers against putting their laptop in the shopping trolley and should brings it to the stalls for sending their commodities instead of holding them. Being lost the wallet is completely unexpected. I only want to admonish everyone of the danger lurking everywhere nothing so much as the Tet holiday. Do you want to be fed up about being lose your money on this holiday?. Say No. You need to be careful of money. A piece of carelessness may create these unfortunate consequences. Remember that money doesn't grow on trees. Good luck for you.

I have to admit that my English level is a bit bad. I want to improve it so that I am determined to post my daily writing with a gleam of hope that fellowships can correct for me. Thank to your comments. Help me.

I have some ideas Hien
=>Today I and my sister have gone to the supermarket together=> ...my sister and I have gone to...

=>When we was buying goods (you can use "groceries") in the supermarket, my sister suddenly cried out and only spoke (=>use past tense) one sentence that she had lost her wallet, which has a Nokia mobile phone inside.

OR=>While we was inside the grocery supermarket, my sister suddenly cried out and said that she had lost her wallet, which had a Nokia mobile phone inside (use "had lost" past perfect)

=> the conner "corner" (misspelling)
=>I can see it=>I could see it (past tense because you're already saw her crying)

=>The thief cleverly hid his face.
=> He took advantage of the situation to merge into the people, who was shopping to prepare for the Tet holiday.
=>Security personnel in the supermarket warned customers not putting their laptop in the shopping trolley and brough it to the security holder.
=> "Being lost the wallet is completely unexpected. I only want to admonish everyone of the danger lurking everywhere nothing so much as the Tet holiday. Do you want to be fed up about being lose your money on this holiday?. Say No. You need to be careful of money. A piece of ca relessness may create these unfortunate consequences. Remember that money doesn't grow on trees. Good luck for you."===>You need to rewrite these sentences instead of "I only want to admonish" you can write something like "Maybe, some people who intend to steal others' property not understanding the feeling of...." You are composing a story, so avoid "Say No"

I fully agree with KathyLala she really knows how to make these projects sound so much better i would go with these changes

what kind of advice is that!?

:-)

my sister suddenly cried out and only spoke one sentence, declaring that she had lose lost her wallet, which had a mobile phone manufactured by Nokia. ---Practice typing this sentence several times to get good habits.

Wow, you are a good writer. Even though you have mistakes, you have a great style of writing, and if you work to improve you will be so good! Look at this sentence, for example:

A small flow of tears from the conner of her eyes streamed out but she still tried to keep back her tears. I can see it. ------I hope you know that this is excellent writing!