Erro em programa php

Estou tendo estes erros nos progrmas que tento baixar para testar:

Warning: main(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\cadastro\index.php on line 33 Notice: Undefined index: link in C:\WAMP\Apache2.2\htdocs\cadastro\index.php on line 33 Warning: main(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\cadastro\index.php on line 36 Notice: Undefined index: link in C:\WAMP\Apache2.2\htdocs\cadastro\index.php on line 36

Warning: mysql_fetch_array(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\vendas\index.php on line 26 Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in C:\WAMP\Apache2.2\htdocs\vendas\index.php on line 26

Warning: main(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\vendas\index.php on line 47 Notice: Undefined index: link in C:\WAMP\Apache2.2\htdocs\vendas\index.php on line 47

Até em um sisteminha desde forum:

Warning: main(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\vend\index.php on line 68 Notice: Undefined index: editar in C:\WAMP\Apache2.2\htdocs\vend\index.php on line 68 Warning: main(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\vend\index.php on line 69 Notice: Undefined index: id in C:\WAMP\Apache2.2\htdocs\vend\index.php on line 69

Warning: main(): It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Sao_Paulo' for '-3.0/no DST' instead in C:\WAMP\Apache2.2\htdocs\vend\index.php on line 314 Notice: Undefined variable: valortotal in C:\WAMP\Apache2.2\htdocs\vend\index.php on line 314 50,01

Estou tentando aprender PHP, mas esta dando muitos erros.