The tan brown branches on your tree are dead twigs and limbs. If you will look towards the bottom of each, you will see a bit of an enlarged green area where it joins the main branch. You should gently prune each of those dead twigs off to just above that.
Besides these dead branches, your tree looks pretty sparse on the foliage. You need to figure out why it is suffering die-back and what is keeping it from growing well. Check to make sure it doesn't have an insect infestation, and that you are giving it enough water (but not letting it sit in a puddle) and that it has enough sunlight (full sun is what citrus prefers in most areas) and feed it monthly with a dilute citrus specific fertilizer.