If you want your pages to appear as you designed them on everyone's computers you have to use fonts that they will have available. Just because you have a particular font doesn't mean that a visitor, especially one who doesn't use the same version of Windows, who uses Mac or other operating systems or who is in another country, will have it.
There are only a few that you can use with any degree of certainty. The official list is shown in the panel.
Although symbols and things like Wingdings feature in both operating systems, they will only be shown correctly in Internet Explorer. Other browsers will display a substitute font, usually not what you will want.
There are many ways to set the size of text on a web page. The best choices are units which enable a visitor to adjust the size of text to suit their own preference. Browsers have an important facility to increase or decrease text size but this will usually not work if you use fixed sizes like points (the unit you'll be familiar with in Office-type applications) or pixels.
The best units are percentages and ems. These can be adapted by a user. Understanding and setting these, though, can require more advanced skills and the range offered by Dreamweaver MX by default is an acceptable and simple way to start. These are sizes 1 to 7. 1 is very small. 7 is very large.
Later versions may offer CSS sizes from xx-small, x-small, small, medium, large, x-large, xx-large. Although not the same as sizes 1 to 7 they are scalable and an acceptable method of sizing text.
If you don't set a font style or size then users will get whatever their browsers offer by default. This will often be Times New Roman in a size that may appear a bit larger than you would normally want, I expect.
You may find that much of your initial work will appear in that style and size until you start making adjustments.
If you want to see exactly how font sizes, browsers and monitor resolutions interact then this link has a very detailed (but heavy going!) explanation.