hi i want to ask you guys, if i import inventory worksheet, it could be add number of quantity item?

the inventory worksheet RESETS the inventory count and costing. To add quantities the tool to use would be an inventory adjustment.

also what is inventory count?

inventory count is used to check inventory. You could use that process instead of the adjustment transaction. But if you already know the variances the adjustment transaction is the easiest

FYI Inventory worksheets cannot be imported, only inventory adjustments, I believe.

It can be imported, but not through the CSV import process. You have to go to Transactions > Inventory > Adjust Inventory Worksheet > Import. There is a sample import file there as the file has to be formatted in a very specific way.