Without actually building your chart it's hard for me to provide support on the report designer. My response below should be a solid starting point but if you have further questions on this specific chart then you should probably contact us for paid support. It helps to have some formal programming background when diving into a custom report.
...break the proposals down by month and then show the number "Closed - Won" and the number "Closed-Lost" or "Cancelled."
From this line I can see you're trying to put together a report with 3 qualifiers based on the Opportunity.Stage field; Closed-Won, Closed-Lost and Cancelled. Qualifiers translates to series in the report designer so you want a bar chart stacked with 3 series'.
Your first series needs to have a data filter to show Opportunity.Stage = closed-won, second series is Opportunity.Stage = closed-lost and last series is Opportunity.Stage = cancelled.
Next comes your argument properties, so how do you want to scale the data (over time)? You mentioned breaking it down by month so your scale type should be DateTime right? Now what argument did you want to scale this data on? (take a cue from that DateTime selection in scale type and guess which field you need to select here).
Lastly your value properties may or may not apply for you - use this section if you need to further process the raw data into something useable. Eg. If I were building a chart that needed to show the total value of the opportunities for a given month, I would use SUM([Opportunity.ExpectedRevenue]). This would total my data by month (based on the argument properties).
Hope this puts you on the right path.