The number intimacy 20 actually shows show 20% out of the tamer's stats will be transferred to your digimon. For example, tamers' attack is 139, so 139*20% = 27.8. After round down, the digimon will increase by 27 attack.

Intimacy can increase and decrease. The range level of intimacy will increase depends on your digimon level :

asiest way to increase intimacy is to use normal attack on wild digimon until your digimon build up the intimacy, and intimacy will only increase 1 by 1 and will stop increasing until it reaches the limit. ( Normal maximum intimacy is 35, however, if you are wearing a costume from cash shop, then the maximum intimacy will increase to 55 )