Ethereum Virtual Machine specific operations, such as accessing storage, retrieve block information, etc, are through EVM specific instructions. Solidity language automatically generates necessary EVM-specific instructions under the hood so as to hide the details from Solidity developers. However, as a compiler backend, the input to EVM LLVM is LLVM IR format, which is unable to hold any language specific semantics that is higher than the C language level. So it is up to compiler frontends to lower language specific semantics onto LLVM IR level.
Intrinsic functions are used to represent EVM-specific semantics in the input LLVM IR. Intrinsic functions are usually higher level representations of architecture-specific instructions. In EVM LLVM, we allow users to leverage EVM-specific instructions that are used to interact with the chain or storage by exposing those EVM instructions in the form of intrinsic functions.