Sharing what I had written sometime ago and yagñā-s and the invocation of agñidēva.

There are many yagñā-s and different devI-s and devatā-s are invoked using different yagñā-s. The word yagña has its root in samskrtam "yaj" which means to worship, honor and revere+

The vēdAngā-s, attached to the Vedic literature, define Yajña as..
Yajña, sacrifice, is an act by which we surrender something for the sake of the gods. Such an act must rest on a sacred authority (āgama), and serve for man's śreyortha.
-Apastamba Yajña Paribhasa-sUtrā-s 1.1

According to chandOgya upanisad..
अथ यद्यज्ञ इत्याचक्षते ब्रह्मचर्यमेव
 तद्ब्रह्मचर्येण ह्येव यो ज्ञाता तं
विन्दतेऽथ यदिष्टमित्याचक्षते ब्रह्मचर्यमेव
 तद्ब्रह्मचर्येण ह्येवेष्ट्वात्मानमनुविन्दते ॥ १ ॥
What is commonly called yajña is really the chaste life of the student +

+ of sacred knowledge,
  for only through the chaste life of a student does he who is a knower find that for only having searched with chaste life of a student does one find Atman (Soul, Self) || 1 ||( abridged it for general understanding).

kalpa-sUtrās lists some of the yajña types:[34]

The Pakayajñā-s — They are the aṣtaka, sthālipāka, parvana, srāvaṇi, āgrahayani, caitri and āsvīyuji. These yajnas involve consecrating cooked items.

sOma-yajñās — Agnistoma, atyagnistoma, uktya, shodasi, vājapeya, atirātra and aptoryama.

havir-yajñās — They are the agniyādhāna, agni hotra, Darśa-Pūrṇamāsa, āgrayana, cāturmāsya, niruudha paśu bandha, sautrāmaṇi. These involve offering havis or oblations.+

+Then you have the five panca mahā-yajñās.
vedavratas, which are four in number, are done during vēdic education.
The sixteen yajñās, which are one-time samskāras or "rituals with mantras", are samskāra (rite of passage): garbhādhānā, pumsavana, sīmanta, jātakarma, nāmakaraṇa+

+annaprāśana, chudākarma/caula, niskramana, karnavedha, vidyaarambha, upanayana, keshanta, snātaka and vivāha, nisheka, antyeshti. These are specified by the Gṛhya-sūtrās. Evolution from external actions (karma-kānda) to internal knowledge (jñana-kānda), were highlighted +

+ in many rituals-related sutras, as well as the Brihadāranyaka upanisad, chandogya upanisad, Kaushitaki upanisad and prānāgnihotra upanisad and other vēdic texts. Both karma-kānda and gñāna-kānda are really important for a seeker of vēdic knowledge.

āgama literally means "tradition" and refers to precepts and doctrines that have come down as tradition. Sri thirumoolar, the siddhār clearly mentioned that the vēdā-s are the path and the āgamā-s are the horses. The immense knowledge of our ancients cannot be taken for granted.

I have been observing many since few days, whose tone and word have been reeking with ignorance and rootless rigmarole.

Hubris is dangerous when half baked knowledge is considered as the benchmark. This arrogance will only create chances for others to mock our way of living.