Geetha,
Save as otherwise expressly provided in this Act, Directors shall be appointed by the Company in general meeting as per section 152 of CA, 2013..
But it is too expensive to company for calling Extraordinary general meeting for appointment of Directors especially for listed companies, to avoid such expenses, Act enabled the Board of Directors if authorized by articles to appoint any person as an additional director at any time who shall hold office up to the date of the next annual general meeting. Next Annual General meeting soon after his appointment, he should be regularized, otherwise he ceased to be director of the Company.
Hence, if your articles permits, Board can appoint any person as additional director upto ensuing annual general meeting as per section 161 of CA, 2013 or if shareholders are appointing any person as director in EGM/AGM, he is deemed to appointed as section 152 of CA, 2013