Tacks are mainly used to secure the ends of pockets and pleats were added reinforcement are needed. When done correctly they are also an attractive feature. Bar tacks are more commonly found in mens tailored garments.
To make a bar tack, stitch several long stitches together along the area required. Then overhand these stitches, catching threads from the fabric at the same time to secure. Cover the whole length with these stitches. Complete the tack by placing smaller bar tacks at either end of the original.