Tar shampoos are designed to cleanse the scalp thoroughly, so the same washing action that removes extra oil can also remove natural moisture from the hair shaft if you scrub the lengths. This formula includes glycerin and allantoin to help the scalp feel less stripped after rinsing, but it is still not a heavy conditioning product. Use it mainly on the scalp and roots. Work the foam into the roots, leave it for a short time, then rinse. Let the suds run down the lengths as you rinse; there is no need to pile shampoo onto the ends.
If your lengths are dry or porous, a practical routine is to apply a conditioner or a mask only from mid-length to the ends afterwards. You can also use a small amount of hair oil or leave-in conditioner on the lengths after towel-drying. Avoid putting these on the scalp if your goal is a deeper scalp cleanse. Some people with dry ends prefer to alternate this tar shampoo with a gentler shampoo, or to pre-treat the lengths with oil before washing. That is a general technique and does not change how the shampoo works on the scalp.
How dry your hair feels also depends on how often you wash. If you use this shampoo more than a few times a week and notice the lengths becoming rough, reduce the frequency or shorten the contact time. The scalp may be fine, but the older parts of the hair cannot regain lost moisture on their own, so when in doubt, condition the lengths and keep the shampoo at the roots.