it's always good to look for a bamboo that is healthy with good strong roots (not rotting)
when you being it home, trim off any mushy roots and run under tap water, washing it very clean.
then place the bamboo in your tank - just stick it in there and have it leaning against a wall, no need to plant it, this will make water changes much easier.
I prefer bamboos over aquarium plants in small tanks as submersed plants leave little room for the betta to swim in.
if the bamboo does it's job properly, your water should remain clear.
Here's a photo of my bamboo :)
make sure the bamboo has a decent light source. you can keep it somewhere where the leaves will be under indirect natural light. the stem doesn't need to be illuminated.