From Google Drive click New > Google Forms.
In the example below, we are creating a form that asks for the current temperature, in celsius. For graphing results later, it's best to stick to only one type of measurement.
Click the "SEND" button at the top, and a dialog window will appear. Click on the chain icon to get a hyperlink and then click the "Copy" button to copy it to your clipboard. This is the link that you will put in the "Form URL" field above.
Click the "Responses" tab, then click on the Google Sheets icon.
Then you will see a dialog window that looks similar to the one below. Select "create a new spreadsheet" and then click "CREATE".
After creating, you should be redirected. Otherwise, you will see a pop-up at the bottom of the screen indicating a new spreadsheet was created. Click to open. You can also find the new spreadsheet from the main Google Drive page.
The new spreadsheet should be empty except for the column headers Timestamp and Temperature.
Below, I have added some data to the spreadsheet so that you can see how it might look when data gets entered, but you can continue to the next step even with no data entered.
Click the gray box in the upper-left corner of the table to highlight the entire table.
Select Insert > Chart to create a new chart. From here you can modify the type of chart (bar, line, scatter, etc.) and other options.
Once you have made your modifications to the chart, you are ready to create an embed code for your chart. Select File > Publish to the web.
When the dialog window appears, select the "Embed" tab. Then select the option named after the table containing the chart (as opposed to the Entire Document option).
Then, click the "Publish" button.
After clicking Publish, the embed code will appear in a text box. Copy this to your clipboard. This is the embed code that you will put in the "Graph Embed Code" field above.