You can import file transactions in two formats, OFX and CSV. You can either import a file that you've developed, or one that you've downloaded from another financial service.
How to import a file
1) Choose which portfolio you want to import into, or choose an existing one.
2) Click Import transaction in the top right corner.
3) Choose file for importing.
4) Before importing the file into the chosen portfolio the columns specified can be adjusted to match the uploaded file: Stock symbol, purchase price per share, number of shares.
5) Click 'Import' found at the bottom of the page to finish the transaction.
Note: You don't have to Import every transaction that you upload. You can tick the boxes to the left of the transaction to indicate what you want imported.
Transferring data: From other financial services/sites to Google Finance
Many other financial services allow you to download your data to a spreadsheet via a 'Download spreadsheet' function. To move your data into Google Finance you simply do the following:
1) Download data from X service.
2) Save data in OFX or CSV format.
3) Import data into Google Finance.
This can also be done between Google accounts.
Most brokerage firms allow you to download historical transactions in .csv format. A .csv file, also known as 'Comma Separated Values' is a plain text file that stores spreadsheet information. If you have your portfolio in an Excel spreadsheet you can also save it as a .csv file to be imported directly.