I’ll address 3rd Orders here;
Generally, Franciscans are an order focuses serving the poor. They serve in soup kitchens, visit the sick etc. The 3rd order community will vary, but this will be the focus of their activity. They will also embrace contemplation, but according to their constitution. They have a formation period and then they make promises.
Discalced Carmelites(OCDS) communities are focused on Contemplative Prayer as taught by St Teresa of Avila and St John of the Cross.
The Constitution for Secular Order Carmelites focus on prayer, living a life of spiritual poverty, chastity and obedience to rightful authority in the Church. They have a strong devotion to the Blessed Mother and wear the Scapular.
Charity and help for the poor is less an activity, but done outside of organized groups as the Franciscans would do.
This website will give you more information and is up to date. Some of the members were formerly members of my community which disbanded over 10 years ago.
Remember, it’s a vocation according to your state in life. Pope John Paul II was a 3rd Order Discalced Carmelite.
As a lay person, you can become a 3rd Order Secular Member.
Jim