Custom Plugin Development and Modification

How pitty,

maybe you can explain me some inputs based on this example

<form action="https://pdr.127.0.0.1.xip.io/contact/" method="post"
      class="avia_ajax_form av-form-labels-visible   avia-builder-el-5  el_after_av_textblock  avia-builder-el-last  "
      data-avia-form-id="1" data-avia-redirect="">
    <fieldset>
        <h3>Send us mail</h3>
        <p class=" first_form  form_element form_fullwidth" id="element_avia_1_1">
            <label for="avia_1_1">Name<abbr class="required" title="required">*</abbr></label>
            <input name="avia_1_1" class="text_input is_empty" type="text" id="avia_1_1" value="">
        </p>
        <p class=" first_form  form_element form_fullwidth" id="element_avia_2_1"><label for="avia_2_1">E-Mail <abbr
                class="required" title="required">*</abbr></label> <input name="avia_2_1" class="text_input is_email"
                                                                          type="text" id="avia_2_1" value=""></p>
        <p class=" first_form  form_element form_fullwidth" id="element_avia_3_1"><label for="avia_3_1">Subject <abbr
                class="required" title="required">*</abbr></label> <input name="avia_3_1" class="text_input is_empty"
                                                                          type="text" id="avia_3_1" value=""></p>
        <p class=" first_form  form_element form_fullwidth av-last-visible-form-element" id="element_avia_4_1">
            <label for="avia_4_1" class="textare_label hidden textare_label_avia_4_1">Message
            <abbr class="required" title="required">*</abbr></label>
            <textarea name="avia_4_1" class="text_area is_empty" cols="40" rows="7" id="avia_4_1"></textarea>
        </p>
        <p class="hidden">
            <input type="text" name="avia_5_1" class="hidden " id="avia_5_1" value="">
        </p>
        <p class="form_element "><input type="hidden" value="1" name="avia_generated_form1">
            <input type="submit" value="Submit" class="button" data-sending-label="Sending">
        </p>
    </fieldset>
</form>

I would like to create a custom form in Enfold style. I create an login field that looks exactly like enfold but because of some ajax magic I couldn’t submit it.
Can you provide me an clean example of the form above that I could your in my page.