Demonstrative pronouns in Reisu are formed when you need to express the distance of something. Eru, for this, literally means 'it close to the speaker' or 'it close to me'. It's formed by the third person pronoun, e, and the suffix -ru. You can also attach -ru to other words.
Example (Maino is in parentheses because it's optional):
Jevaru (maino) larelai.
This flower is beautiful.
Implies that the speaker is holding or next to the flower.
Attaching -ru to a noun is the closest Reisu gets to forming an article. So sometimes -ru is attached simply to call attention to the noun. So the above sentences could also be translated as 'The flower is beautiful'.
To form the concept of 'that' or 'those' we use the suffix -vo. Evo literally means 'it close to the listener'.
Topavosa sukaxi yaivi.
Those problem won't go away easily.
Implies that the listener is the one with the problems.
This is a third and final declination, -ve. This is for when things are far from the listener and the speaker.
Emodovesa maino gurage!
Those people are starving!
Implies the people are far from both the listener and the speaker.
In conclusion use -ru, -vo and -ve when you express the proximity of something.