Allah (ﷻ) is our Creator, Sustainer, the One & Only God. He sent numerous Messengers and Prophets (may the peace & blessings of Allah be upon all of them) throughout human history to various nations on earth in order to guide them to the correct path. Muhammad (ﷺ) was the last one in a long chain of the Messengers & Prophets. He was sent as a mercy to mankind for through him Allah sent the final guidance to mankind and preserved it in the Quran & Sunnah. The guidance brought by the final Messenger (ﷺ) was preserved and the responsibility of ensuring the guidance reaches everyone was given to every Muslim until the Day of Judgment through Dawah.
Dawah is an invitation to Allah and His religion Islam. The way human beings behave, we either affect others (with our words and actions) or we are affected by others (because of their words and actions). Either we give Dawah to others or we receive the Dawah from others. This is because if we are not actively seeking to convey the message of guidance and salvation to others, we are receiving messages of whatever the world has to offer. To be beacons of the light of guidance is to be safest from the darkness of misguidance.
Islam is essentially a way of life. Therefore the best invitation to Islam is through actions, not through words. When people see Muslims living Islam, they will be attracted towards it. Words alone are not enough to invite people to Islam, especially if they see a contradiction between our words and our actions. Therefore the best form of Dawah is through our own practice of Islam in every aspect from worship (which is our relationship with Allah), to dealing with individuals & societies (which are our relationships with other human beings). These dealings include both in our interpersonal relationships and our business dealings.
If our worship and our relationships with human beings are both sound, then our Dawah is in line with the teachings of Islam and is effective. Otherwise, our Dawah is deficient and not very effective.
And Allah knows best.