How To Use APEX:COMMANDBUTTON In Visualforce Page?

<apex:commandButton>:

 Buttons are very important in any page and they are the means using which a user interacts with the system to perform some actions such as Save, Update, Create, Delete, Cancel etc... 

This tag helps us to create buttons.The action that has to be executed when the button is pressed depends on the ACTION attribute specified in this tag. The action that is specified needs to be defined in the controller that is used in this pages controller attribute of the page tag. Once the action is performed the page would navigate to a different page or display the same page based on the PageReference variable that is returned by the action.

An < apex:commandButton > component must always be a child component of the < apex:form > tag. 

syntax:
<apex:commandButton action="{!save}" value="Save" id="save"/>

This tag supports following attributes:

Attribute	Description
Id	An identifier that allows the commandButton component to be referenced by other components in the page.
Image	The absolute or relative URL of the image displayed as this button. If specified, the type of the generated HTML input element is set to "image."
Immediate	A Boolean value that specifies whether the action associated with this component should happen immediately, without processing any validation rules associated with the fields on the page. If set to true, the action happens immediately and validation rules are skipped. If not specified, this value defaults to false.
onblur	The JavaScript invoked if the onblur event occurs that is, if the focus moves off of the command button.
onclick	The JavaScript invoked if the onclick event occurs that is, if the user clicks the command button.
oncomplete	The JavaScript invoked when the result of an AJAX update request completes on the client.
ondblclick	The JavaScript invoked if the ondblclick event occurs that is, if the user clicks the command button twice.
onfocus	The JavaScript invoked if the onfocus event occurs that is, if the focus is on the command button.
onkeydown	The JavaScript invoked if the onkeydown event occurs that is, if the user presses a keyboard key.
onkeypress	The JavaScript invoked if the onkeypress event occurs that is, if the user presses or holds down a keyboard key.
onkeyup	The JavaScript invoked if the onkeyup event occurs that is, if the user releases a keyboard key.
onmousedown	The JavaScript invoked if the onmousedown event occurs that is, if the user clicks a mouse button.
onmousemove	The JavaScript invoked if the onmousemove event occurs that is, if the user moves the mouse pointer.
onmouseout	The JavaScript invoked if the onmouseout event occurs that is, if the user moves the mouse pointer away from the command button.
onmouseover	The JavaScript invoked if the onmouseover event occurs that is, if the user moves the mouse pointer over the command button.
onmouseup	The JavaScript invoked if the onmouseup event occurs that is, if the user releases the mouse button.
rendered	A Boolean value that specifies whether the component is rendered on the page. If not specified, this value defaults to true.
reRender	The ID of one or more components that are redrawn when the result of an AJAX update request returns to the client. This value can be a single ID, a comma-separated list of IDs, or a merge field expression for a list or collection of IDs.
status	The ID of an associated component that displays the status of an AJAX update request. See the actionStatus component.
style	The style used to display the commandButton component, used primarily for adding inline CSS styles.
styleClass	The style class used to display the commandButton component, used primarily to designate which CSS styles are applied when using an external CSS stylesheet.
tabindex	The order in which this button is selected compared to other page components when a user presses the Tab key repeatedly. This value must be a number between 0 and 32767, with component 0 being the first component that is selected when a user presses the Tab key.
timeout	The amount of time (in milliseconds) before an AJAX update request should time out.
title	The text to display as a tooltip when the user's mouse pointer hovers over this component.
value	The text displayed on the commandButton as its label.

Visualforce Example:

<apex:page standardController="Account">

    <apex:form >

        <apex:pageBlock title="My Content" mode="edit">

            <apex:pageBlockSection title="My Content Section" columns="2">

                <apex:inputField value="{!account.name}"/>

                <apex:inputField value="{!account.site}"/>

                <apex:inputField value="{!account.type}"/>

                <apex:inputField value="{!account.accountNumber}"/>

            </apex:pageBlockSection>

            <apex:pageBlockButtons >

                <apex:commandButton action="{!save}" value="Save"/>

            </apex:pageBlockButtons>

        </apex:pageBlock>

    </apex:form>

</apex:page>