Woven fabrics are manufactured on room sized looms that have warp (lengthwise) and weft (crosswise) threads. The looms are "warped" with base threads first that run the length of the loom, and then the weft threads are woven under and over the warp threads, kind of like you'd see on a basket. Woven fabrics typically have very little stretch unless special elastic fibers have been added to make them have a little more give. Woven fabrics can fray if the edges are not finished. Sometimes this is a desirable feature, such as cut-off jean shorts, and sometimes it's an annoyance, like if the stitching comes out of the hem of a shirt. Garments made with woven fabrics usually have seams and darts to shape the fabric so it will fit over the curves of the body a certain way, along with some sort of closure (zipper, buttons, snaps, ties, etc.) that allows the wearer to put it on and take it off with ease.
Knit fabrics are made on room sized knitting machines, where one long strand of fiber is first looped onto hooks. The machine then moves sets of hooks over and under each other to knit the strand of fiber into rows that become a large piece of fabric. If you've ever seen a friend or someone in your family knitting or crocheting something, you've seen this happen on a much smaller scale (two needles or one hook). Knits can be slightly stretchy or extremely stretchy, depending on the fiber and how tightly the fabric has been knitted. Knits ravel instead of fraying because they are one continuous thread. If you pull on a loose thread on a knit garment, you may end up with a very large hole or a shorter garment as the rows come undone. Garments made with knit fabrics often do not need any shaping or closure because they will stretch to accommodate being pulled onto and off of the body.
Sewing patterns usually specify whether they are designed for wovens or knits. Some pattern designs lend themselves to either, but you would need to make certain adjustments first to account for more stretch or no stretch.
