Many people begin as inquirers: they visit services, read, ask questions, and speak with a priest. If the person continues seriously, the priest may receive them as a catechumen, someone preparing to enter the Church.
Start with worship
Orthodoxy is learned most deeply by worshiping with the Church. Attend the Divine Liturgy, and if possible Vespers or another service, for several weeks before trying to understand everything intellectually.
Speak with a priest
Books and websites can help, but reception into the Church happens through a parish and bishop, normally with the guidance of the local priest. The exact path can differ depending on background, baptismal history, and local practice.
What catechesis includes
Catechesis may include the Creed, the Holy Trinity, Christ, Scripture and Tradition, the Divine Liturgy, prayer, fasting, confession, parish life, and the moral life. It is not just information; it is formation.
Do not try to self-receive into Orthodoxy through online content. Visit a canonical Orthodox parish and speak with its priest.