How and where can I start an online digital marketing campaign?

Have a product/service. 

Locate target audiance, (next step depends on it)

Decide which channels online will you be using, social media, online platforms/websites, etc etc 

Consistancy and innovation in context. 

just pay payment google, facebook, and other

Before you go digital, there are 3 tasks you must complete.

1. Segment your market. Obviously, you cannot serve everyone.

2. Target. Your target (customer(s)) should be well described and consumer behavior well explained. If you miss this, everything that follows will be WRONG and wasted effort.

3. Position your product (goods or services) in a way to clearly communicate a value proposition.

Then go digital!

How do ?? The preparation of marketing campaign organized by which the objectives and the place is determined on the basis of the company's products and the market to be expanded and the target audience and the language of communication with the public through the content of good and simple and

An effective campaign demands a great deal of time, patience and planning Before you can plan any campaign, you need to understand and outline your overall marketing goals. Establish SMART (Specific, Measurable, Attainable, Realistic and Timely) goals for best results. Your goal might be to gain at least 10 new clients a month or to sell 10 products per week, or to increase your individual income by 30 percent this year). Goals can be based around sales, customer satisfaction or profits. Describe your product or service and its features and benefits in detail, as well as how it’s different from the competition. Focus on all of the key features for your product(s) / service(s), including pricing, service, distribution and placement. Collect, organize and write down this information.

define your customers 

chose your targets

monitor your conversion rate 

setup your budget

creating your ad content 

tracking and monitoring your ad 

use social media related to your products and customers 

Generally people use the campaigns on facebook, Google, Twitter - but I'd suggest you to create your plan and decide what you actually looking for. If you looking for the leads, please choose and create your audience wisely and target the required regions, gender, country what so ever is your requirement. I work on Facebook and Google (Youtube preferred if you have Video Marketing) to create my campaigns and they work well.

Can you elaborate your question more.

Various platforms to use for an online marketing campaign at low cost and reach many people are Facebook ads and Google AdWords.

Usually sites like Amazon are allowed to do this within their organization

It's all about your main objectives and where your audience be online. For example if your objective is collecting leads and your business based in Dubai wants to target KSA residence so you have to start your campaign with twitter and send your audience to a landing page to get a leads. But it depends on your budget as facebook gets more leads with lower cost than twitter but maybe not the better result. So you have to start writing down your plan and study the place your audience might be used online for a better results suits your budget.

You can start yourself read youtube channels on digital marketing how to set up a strategy and advantages of digital marketing once you know the basic you can do the rest. It's not that difficult, a little effort can help you.