Receiving input from RS232 and reading it with Arduino board
A ready-made RS232 shield for the UNO such as the one I linked would be the quickest way to get going collecting data (it was the first search hit; I have no experience with the particular product or vendor.)

If learning and doing are more important, you could make up some RS232 &lt;-> 5v logic level-shifters and write or find a software UART to read the bit-stream.