For anything but a very simple garment (loose fitting, no darts, no fitted sleeves) you probably need a pattern.
Simplicity Patterns are usually easy to follow. The website is also fairly easy to navigate. There is not a huge selection on there, however.
This site has a good selection of patterns from the major manufacturers, and is also easy to navigate, and offers up to 50% discount on retail proice which is worth having! I think I may have bought from them before. I've had good results with Simplicity, New Look and Butterick patterns. Vogue Patterns are nice, but tend to be more complicated.
I don't find this site as easy to use, but they have some quite cool stuff in their haberdashery section, so I may be making a purchase soon.
I think I've bought other stuff from them before. The site is easy to use, and they have the dvantage, like Jaycotts and Sew Direct of selling other things you might need, which may save you a bit on shipping.
Free patterns and instructions. This site links to other sites and blogs, patterns and links are variable. This is one to spend time browsing one day when you've got nothing much else on, to see if you can find anything useful.
And a bit of fun!
It wouldn't be a me post without a bit of costuming! Remember the bonnet I brought to class? Here are some instrctions for making one!!
And, slightly more complicated, but these are the instructions I actually used.