StringPart

StringPart["string",n] gives the nth character in "string".

StringPart["string",{n1,n2,…}] gives a list of the nith characters in "string".

StringPart["string",m;;n;;s] gives a list of the characters in "string" from the mth through the nth in steps of s.

StringPart[{s1,s2,…},spec] gives the list of results for each of the si.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.