Mantra is sound/vibrations of energies related to deities (The deity itself). Example: om gan ganpataye namah.

Yantra means device; it is a kind of physical manifestation of the deity. It can be a geometric diagram. Example: Meru Yantra — a 3D pyramid-shaped representation of Sri Chakra symbolizing divine feminine energy.

Tantra basically means method or technique; in this context, “a method of worship”. The main aim of tantra is similar to all of the other Hindu philosophies, i.e. moksha/Nirvana. Tantra is not limited to but mostly used for the worship of Devi and her associated devatas. Tantra can involve a combination of mantras and Yantras.

Sadhana is the actual practice that the seeker (sadhaka) performs — the discipline through which the teachings of Tantra (or any other path) are realized in daily life. Without doing (tantric or any other) Sadhana, Tantra remains theoretical. Without Tantra (or another path), Sadhana lacks a proper method or structure.

So, Sadhana gets added as a suffix to tantra and other practices. The seeker/practitioner is the sadhaka.

Yoga is a group of physical, mental, and spiritual practices or disciplines that originated with its own philosophy in ancient India, aimed at controlling body and mind to attain liberation / moksha.

Patanjali is a revered ancient Indian sage and philosopher (c. 2nd century BCE – 4th/5th century CE) credited with compiling the Yoga Sutras.

Modern day yoga practitioners often practice varying postures, breathing techniques and meditation practices.

Kriya Yoga is a yoga system which consists of multiple levels of pranayama, mantra, and mudra, intended to rapidly accelerate spiritual development and engender a profound state of tranquility and God-communion.

Popular people who spread Kriya Yoga are: Mahavatar Babaji, Lahiri Mahasaya, Paramahansa Yogananda.

Mahavatar Babaji is said to be an immortal guru living in the Himalayas who has trained various devotees in Kriya Yoga.

Paramahansa Yogananda is a popular guru who is famous for spreading Kriya Yoga in the West. He also wrote a famous best-selling book — Autobiography of a Yogi.

A Guru is a revered spiritual teacher, guide, or master who dispels the darkness of ignorance (gu = darkness, ru = remover) and leads disciples (shishyas) toward self-realization, moksha (liberation), and deeper understanding of scriptures.

There is a staunch belief to start certain religious practices only with the guidance of a guru, since some practices when done wrong are believed to bring negative effects.

In Astrology, Guru refers to the planet Jupiter (Brihaspati). Guru represents knowledge and education. A strong Guru is considered one of the hallmarks of a strong astrology chart for a person, since it can help with removing a lot of doshas.