Thanks.Ok so HD is not HD. HD is a broad term for a resolution meeting or exceeding 720p. There are several types of HD that are separated by their industry terms. 720 = HD / 1080p = Full HD / 1440p = 2K HD / 2160p = 4K Ultra HD. Your MacBook as a resolution of 1680x1050. Its just below 1080p which is 1920x1080, so your screen is better then "HD" but does not meet the "Full HD" resolution.
While you may be streaming HD your not going to see everything the picture could be if its a 1080p or higher stream. Netflix for example has some 720, that will look better on your screen with the up scaling it will do, but its 1080p content will not look as good as it could, but will still look better than the 720p stream. YouTube offers 2K and 4K content now. Your screen will never be able to tell the difference between the 1080p setting and the 2/4K setting, it should look the same when viewing full screen.
The retina MacBooks run between 2K to 3K depending on what one you get. So the MacBook has a 2K display, The 13in MBP has 2560-by-1600 so its like 2.5K, the 15in MBP has 2880-by-1800 that generally is classified as 3K. Both the MBP's could watch 4K content, it will not be as good as an actual 4K screen but it will look a lot better than 2K. The MB has a 2K screen so it will only ever be able to display a max of 2K/1440p and will have no gain by choosing 4K.
In closing your screen will do HD, just not 1080p "Full HD". It should still look very good, just not as good as a 1080p screen or the Retina Macs.