For the first sentence, the correct way to say it should be: "Creo que no tienes champu." (I believe you don't have shampoo.) Therefore, it is not subjunctive.
tienes is the indicative form - as in you have now; tengas is subjunctive form - as in you would have if... (condition)
The second sentence should read: "Yo quiero que me des una pluma." (I would like you to give me a pen.) It is a subjunctive if you write it the way I show above. It shows command.
The subjunctive mood is when the verb form is used to express a wish, a suggestion, a command, or a condition that is contrary to the fact. In Spanish, for most verbs, the present subjunctive is formed by following these 3 steps:
- Begin with the yo form of the present indicative.
- Drop the -o ending.
- Add the following endings:
-ar verbs: -e, -es, -e, -emos, -en
-er and -ir verbs: -a, -as, -a, -amos, -an
I hope this was helpful.