is there any way to use 2 different send buttons one for paypal payment and other simply for send the submission

i need to create 2 send buttons one for paypal payment (i've already got it) and other that appears when one of the customers select in field "payment method" = "pay in cash upon arrival" i need one button that appear only to sen the reservation

Two buttons are not necessary.  Set up a field that asks whether they will be paying via PayPal or via cash.  Then conditionally show the PayPal field depending and submit button or just the submit button depending on what is selected:

http://www.jotform.com/help/57-Smart-Forms-Using-Conditional-Logic

i've been triying tu put the conditional rule about the button, the normal function of the button it's to send to the paypal page to pay it but the only thing that i need when the customers select the "pay in cash" on the field "payment method" it's when you press the "reserve" button go directly to the "thank you" page but i don't know haw to create that rule.... 

When you do not want your users to be redirected to PayPal, you will have to use the conditional rule to hide the PayPal payment tool from the form. We have a guide dedicated to this setup here:

http://www.jotform.com/help/120-How-to-set-up-paypal-along-with-other-payment-options

Essentially, when the PayPal option is conditionally shown to the user, they will be redirected to PayPal. When this field is hidden from the form, it will go directly to your "thank you" page. So you will only need to use a show conditional rule, and show PayPal payment tool if PayPal is selected in your "payment method" field.

Please take a look at the above linked guide, and kindly let us know if you need any further clarifications or assistance.