You can collect pollen directly or collect pollen containing flower stamens, dry them at around 30C (putting for example under a lamp).
Stamens than are gently grinded by forceps, debris is removed and pollen be put in a small envelope made from paper. You can put several grains of rice to enhance drying.
The envelope should be put in hermetically closed vial with a small packet of silicagel (these packets are often delivered with new electronic devices and even shoes).
Silicagel before the use should be dehydrated by heating in a microwave oven for 5 minutes and cooled to room temperature.
The vials are secured with plastic films used in grafting like Parafilm or Buddy-tape.
You can store the vial with pollen for up to three months in a refrigerator or up for one year at -20C freezer.
Before the opening vials should be equilibrated at room temperature to prevent pollen wetting.