What do these sentences about nginx implementing rewrite mean?

Question

    if (-f $request_filename/index.php){
            rewrite (.*) $1/index.php;
    }
    if (!-f $request_filename){
            rewrite (.*) /index.php;
    }

Answer 1

  if (-f $request_filename/index.php)
#如果存在文件$request_filename/index.php
{
            rewrite (.*) /index.php;
            #那么执行这条 rewrite
            # 代表上面if里匹配的
    }
    if (!-f $request_filename){
    #如果不存在文件$request_filename
            rewrite (.*) /index.php;
            #那么执行这条 rewrite
    }