why such so many single quote used in query - sql

Question

I am searching a query which generate html table. I found this query, but I can not understand what is use of such so many single quote used here and
why all code create in variable. I am new in sql please help me.
BEGIN
SET NOCOUNT ON;
IF #orderBy IS NULL
BEGIN
SET #orderBy = ''
END
SET #orderBy = REPLACE(#orderBy, '''', '''''');
DECLARE #realQuery NVARCHAR(MAX) = ' //this is variable which take all query as string
DECLARE #headerRow nvarchar(MAX);
DECLARE #cols nvarchar(MAX);
SELECT * INTO #dynSql FROM (' + #query + ') sub; -- how this temp table create
SELECT #cols = COALESCE(#cols + '', '''''''', '', '''') + ''['' + name + ''] AS ''''td''''''
FROM tempdb.sys.columns
WHERE object_id = object_id(''tempdb..#dynSql'')
ORDER BY column_id;
SET #cols = ''SET #html = CAST(( SELECT '' + #cols + '' FROM #dynSql ' + #orderBy + ' FOR XML PATH(''''tr''''), ELEMENTS XSINIL) AS nvarchar(max))''
EXEC sys.sp_executesql #cols, N''#html nvarchar(MAX) OUTPUT'', #html=#html OUTPUT
--in coalesce why so many '''' used
SELECT #headerRow = COALESCE(#headerRow + '''', '''') + ''<th>'' + name + ''</th>''
FROM tempdb.sys.columns
WHERE object_id = object_id(''tempdb..#dynSql'')
ORDER BY column_id;
SET #headerRow = ''<tr>'' + #headerRow + ''</tr>'';
SET #html = ''<table border="1">'' + #headerRow + #html + ''</table>'';
';
EXEC sys.sp_executesql #realQuery
,N'#html nvarchar(MAX) OUTPUT'
,#html = #html OUTPUT
END
Above query is working fine, but I can't understand it.