If you only have information in Box 1a and Box 5, you will have to get the information for the other boxes. You will need to have the acquisition date and the date of the sale. What Box 5 means is an SEC designation under which the cost basis of securities that are small and of limited scope may not be reported to the IRS. The adjusted cost basis of non-covered securities is only reported to the taxpayer, and not the IRS.
You will need to know your cost basis otherwise you will be paying tax on the amount of the proceeds.
You might want to contact your broker to see if they can provide you with the missing information.
