When sewing garments and accessories darts are an essential technique to master in order to create a great fit/shape. Darts can be straight or curved depending on desired effect. A straight dart will give you an easier, looser fit while a curved dart will be more form fitting.
Check out this tutorial on one of my personal favorite sites, Sew Mama Sew. This blog is amazing! Full of great tips, tricks, and tutorials. I have to admit I like to check it out every day! It goes over the importance of darts in the fit of a garment with and easy to follow picture tutorial and instructions. The triangle areas seen in the photo below represent the actuall dart placement on the garment pieces, in this case a dress. Darts will be used in this instance to take in the fabric where each dart is placed to create a formed fit.
Joanna over at Stardust Shoes has a great tutorial showing you how to take in your pants using butt darts.
Check out this fun and elegant pleated bag tutorial from Lisa Lam (which is funny because that's my name too!!) at U Handbag. With a change of fabric, this would be perfect for a wedding or holiday party. In this instance, the darts give the bag a fun shape and detail.
Threads Magazine has a great video collection. Included in this collection are two videos that would be useful for marking darts and sewing darts in your fabric projects. This collection is a super valuable tool for novice and intermediate sewers.