July 1:
Sales Dept. placed Purchase order to Japan for 100 units of navigation system. Unit price was $400 per unit. What is the accounting entry?

We established a trading company. Sponsor gave us $100,000. What is correct entry for book?

July 15:
Sales dept. received invoice from Japan. Invoice amount was $40,000 but goods were still on the water. At this moment, what is the correct entry for the book?

July 31:
Invoice due date is on July 31. Goods were still on the water but we paid on due date. What is the correct entry for the book?

August 15:
Goods arrived in our warehouse, but only 50 units were received. At this moment, what is the correct entry for the book? Still missing 50 units. What is the correct action?

August 20:
Finally rest of the goods arrived. What is thew correct entry for the book?
What is the important point at this moment?

August 31:
We received order from customer in Mexico. 100 units and unit price is at $500. We shipped on same date and issued sales invoice. At this moment, what is the correct entry for the book?

In the result of this transaction, what happens on Balance sheet and P&L?

September 30:

The customer in Mexico paid but the amount was $49,900. In the result of investigation, we found that bank charge had been deducted.
In the case of we owe bank charge, what is the correct entry?

This sounds like homework. Please see the guidelines for posting homework problems:
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You also need to learn the rules and the concepts, or ask questions about what you don't understand, and then try to that to your problems, not just post here every entry that you have.