Welcome to the forums!
Congratulations on your new budgies! Is this your first time owning them and do you have sufficient knowledge of the species as a whole in order to go through the task of breeding?
Breeding budgies or any living being for that matter, is a big responsibility and requires a deep knowledge and a whole lot research should be done prior to allowing a couple to breed.
It's not advisable to let a recently acquired pair to breed, so please do not give them a nest box nor anything that they could use as nest yet.
It takes time for budgies to settle into a new house and environment. It's important to know how old the pair is before setting them up for breeding. The bare minimum required age for them to breed is 1 year of age and the pair needs to be put on a good breeding diet prior to placing the nest box in the cage and the pair needs to be in top physical health and condition to go through mating laying eggs and raising their young.
Your budgie on the left is a male and while his cere is showing the mature colour, he still looks to be under a year old.
Your other budgie is very young at about 3 months old (doesn't appear to have gone through the baby moult yet). If you post a better close up photo showing the whole beak/cere area, we can help you out in determining its gender. From that pic, it seems the cere is somewhat purplish, so you may have another boy there.