Use these pronouns when you want to refer to something. The pronouns have both singular and plural forms. 

Use the pronoun tämä/nämä, when the object is close to you and you are able to touch it.

Tämä ruoka on tosi hyvää.
This food is really good.

Nämä puut ovat niin vanhoja.
These trees are so old.

Use the pronoun tuo/nuo when referring to a thing further away. The object is not close, but you can see it and point at it.

Mikä lintu tuo on?
What bird is that?

Nuo sienet ovat myrkyllisiä, varo!
Those mushrooms are poisonous, watch out!

Use the pronoun se/ne, when you refer to something that has been mentioned earlier.

Kokeile avantouintia. Se on ihanaa!
Try ice swimming. It is lovely!

Se vihreä yrtti, tilli.
The green herb, dill.

Ne ovat kauniita kukkia.
They are beautiful flowers.

When talking about wild animals, birds or fish, use the pronoun se.

Kato, puussa on orava. Se on niin söpö!