In SR 6 too?
You were not very specific in your original question ;-)
During chargen in SR6 you only have free spells, rituals or power points (depending on how you use magic) and you can only spend customization karma on qualities, skill advancement, attribute advancement and nuyen.
For SR6 there are not many summoning specific options (yet). If you don't plan on casting any spells, using any powers or doing any preparations then you might as well start with a low Magic or Resonance priority and instead raise your magic rating with adjustment points from Metatype prioritization. I would advance against an aspected conjurer, as a summoner you will almost always be better off as a full magician (which give you astral projection and perception but no power points) or mystic adept (which give you access to power points and ability to pay for astral perception, but no astral projection).
You can buy spirit foci but it doesn't seem as if you may spend karma on binding them until post chargen. They will act as positive dice pool modifiers of force rating to your conjuring skill when summoning spirits (note that skills in 6th edition are limited to a bonus of +4 so no need to get stronger spirit foci than that, but you use different foci depending on spirit type). They cost force x 2 karma to bind.
You can also buy a banishing focus that you may spend post chargen karma to bind. In this case you gain a free edge when banishing a spirit but only if the banishing focus have a force equal or higher than the spirit you attempt to banish. It cost force x 2 karma to bind.
The maximum number of foci you can have is limited to your (adjusted) magic rating.
The total number of force of all your combined bound foci is limited to your (adjusted) magic rating x 5.
