A) If you are a manufacturer, you have to follow these 6 steps to affix a CE marking to your product:
1.Identify the applicable directive(s) and harmonized standards
2.Verify product specific requirements
3.Identify whether an independent conformity assessment (by a notified body) is necessary
4.Test the product and check its conformity
5.Draw up and keep available the required technical documentation
6.Affix the CE marking and draw up the EU Declaration of Conformity
Your product will belong to one or more product groups in below. If you choose an appropriate product group for your product, that will be a Directive which your product should follow.
  • Active implantable medical devices
  • Appliances burning gaseous fuels
  • Cableway installations designed to carry persons
  • Construction products
  • Ecodesign of energy related products
  • Electromagnetic compatibility
  • Equipment and protective systems intended for use potentially explosive atmospheres
  • Explosives for civil uses
  • Hot-water boilers
  • In vitro diagnostic medical devices
  • Lifts
  • Low voltage
  • Machinery
  • Measuring Instruments
  • Medical devices
  • Noise emission in the environment
  • Non-automatic weighing instruments
  • Personal protective equipment
  • Pressure equipment
  • Pyrotechnics
  • Radio equipment
  • Recreational craft
  • Restriction of Hazardous Substances in Electrical and Electronic Equipment
  • Safety of toys
  • Simple pressure vessels
A harmonized standard is a European standard developed by a recognised European Standards Organisation: CEN, CENELEC, or ETSI. It is created following a request from the European Commission to one of these organisations. Manufacturers, other economic operators, or conformity assessment bodies can use harmonized standards to demonstrate that products, services, or processes comply with relevant EU legislation.The references of harmonized standards must be published in the Official Journal of the European Union.
You can find the best proper standard for your product through below link.
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As part of conformity assessment, the manufacturer or the authorised representative must draw up an declaration of conformity (DoC). The declaration should contain all information to identify:
• the product
• the legislation according to which it is issued
• the manufacturer or the authorised representative
• the notified body if applicable
• a reference to harmonized standards or other normative documents, where appropriate