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Pascal strings are first-class. FreePascal has multiple string types — for now, just use the default string (which in modern FPC is AnsiString, dynamically allocated).

var
    s, t: string;
begin
    s := 'Hello';
    t := ' Pascal';
    WriteLn(s + t + '!');                  { Hello Pascal! }
    WriteLn(Length(s));                     { 5 }
    WriteLn(Copy(s, 2, 3));                 { 'ell' (1-indexed!) }
end.

Key string operations:

• Length(s) — character count
• s[i] — character at position i (1-indexed!)
• s + t — concatenation
• Copy(s, start, count) — substring
• Pos(needle, haystack) — index of first match (0 if not found)
• Insert(value, target, pos) — insert in-place
• Delete(s, pos, count) — remove in-place

SysUtils for more — uses SysUtils; at the top:

• UpperCase(s), LowerCase(s)
• Trim(s), TrimLeft(s), TrimRight(s)
• StringReplace(s, old, new, [rfReplaceAll])
• Format('%s = %d', [name, value]) — printf-style
• IntToStr(n), StrToInt(s)
• FloatToStr(x), StrToFloat(s)

uses SysUtils;

var s: string;
begin
    s := '  hello world  ';
    WriteLn('[' + Trim(s) + ']');                          { [hello world] }
    WriteLn(UpperCase(s));                                  {   HELLO WORLD   }
    WriteLn(StringReplace(s, 'world', 'Pascal', [rfReplaceAll]));
    WriteLn(Format('len=%d', [Length(s)]));                 { len=15 }
end.

Iterating characters:

for i := 1 to Length(s) do
    WriteLn(s[i]);

for c in s do                                              { for-in (FPC 3.x) }
    WriteLn(c);

char type — single character (as in 'a'):

var c: char;
begin
    c := 'A';
    WriteLn(Ord(c));        { ASCII code: 65 }
    WriteLn(Chr(97));        { 'a' }
end.

Old-school string[N] — fixed-size, 1-indexed with length byte. Mostly historical; modern FPC's string is dynamic.

For heavy text processing, FreePascal also has WideString (UTF-16, COM compatible) and UnicodeString (FPC 2.7+, UTF-16/UTF-8 depending on platform). For learning, plain string is fine.