Mantra ( मंत्र) – is a sacred utterance, a syllable or group of words believed to have psychological and spiritual powers. Example – Gayatri Mantra, Om, Shanti Mantra
Shloka (श्लोक) – A pair of successive lines of verse, typically rhyming and of the same length. Most Hindu scriptures are written in forms of slokas. Mahabharata, Ramayana & Upanishads etc.
Suktam (सूक्त) – Suktam is derived from सु + उक्त (speak, recite) means which is well recited (सुष्ठु उक्तम्)
Each Veda is divided into mandala consists of hymns called suktam intended for various rituals. The suktam in turn consist of individual sloka’s . Example – Nasadiya Suktam, Purusha Suktam , Shree Suktam
Stotram (स्तोत्र ) – It is written in poem like structure expressing praise and personal devotion to a deity. Many Stotram hymns praise aspects of the divine, such as Devi, Shiva, or Vishnu. Example – Panchakshara Stotram, Ram Raksha Stotram, Saraswati Stotram
Stuti (स्तुति) – Stuti is derived from “स्तु” dhatu means to pray or to praise. Any prayer offered to praise is called Stuti. It can be done by reciting mantra, suktam, Stotram or bhajan. Example – Laxmi Stuti, Shiva Stuti