Put the tip of your tongue between your top and bottom teeth and press down lightly. Now force air past your teeth and you should get the 'th' sound. Now pull your tongue back, keeping it against the rook of your mouth. You have to push air between the top of your tongue and roof of your mouth. Practice each individually and then combine the two :)

Month/months sound pretty similar. How do you know which one people mean? Usually from context. For example, you would say “I know her many months.” And I would understand you perfectly well even if you say “many month” because of the keyword “many”.

You should listen to these here: http://www.forvo.com/search/month/ http://www.forvo.com/search/months/ That won't tell you how to pronounce them, but you won't be able to pronounce them until you can hear the difference! You could upload your own pronunciation to "www.vocarro.com" and we could tell you if you're pronouncing them correctly.

By the way... please don't confuse "being understood" with "saying it correctly". The native speakers here are more than happy to show you the right way to use their language, so there's no need to accept "second best" (ie. sentences which are understandable but clearly wrong). :)

Hi Jacob, make sure that you are pronouncing the "th" sound absolutely correctly. Some learners use "s", "t", "z" or "d" as a substitute, and it never sounds natural. Sometime this substitution makes the speaker mispronounce words. Anyway, once you have the "th" sound right, practise the transit from θ to S. You need to practice it both ways. Good luck!