@srdceleva you mean how they sacrifice all kinds of stuff in the old testament? Only sacrifice that can be observed throughout Slavic world is bread.
By all records Slavic religion was your typical Indo-European polytheistic religion. You can find the same symbolism and circular patterns all over Europe. Theory of Iranian influence (certainly not base as you wrote in your first comment) is based on theistic dualism present in Iranian faith as @”South Slav” already wrote. He also wrote the main argument for that – Belobog/Černobog dualism. Problem with that is that there’s no record of Belobog or any kind of dualism in pre-Christian Slavic faith. Černobog is mentioned pretty late, in 12th century he’s mentioned to exist among few non-Christianized Polabian tribes. By that time they were surrounded by Christians. Dualism came to Slavs with Christianity. Ancient Slavs for sure had contact with some Iranian groups, but Slavic faith being practically form of Zoroastrianism is pretty big stretch. There’s no evidence that Slavs ever viewed a deity as purely good or bad.
Perun (as a word and as a deity) evolved from perkwunos, which reconstructed Indo-European deity. Deities with similar names and function could be found among Balts, Thracians and Fins (through Balts). The name also survived in Germanic faith in the name of Thor’s mother, Fjörgyn.
Svarog as an idea is way too complicated for this comment