You could build a form as simple as the following one. Of course you could add as much form fields as you want
Name an email field _reply_to to set it as a Reply-to in the email you will receive.
This will allow you to easily reply to the users who fill your form.
To protect your form from unwanted submissions, add the following field to your form.
Its value must remain empty. It prevents simple bot from spamming your form
For a much better ant-spam protection using Google reCaptcha add the following lines to your form.
Finally enable reCaptcha support in your form settings
In order to be able to upload files. You must set the enctype attribute to multipart/form-data.