First day of Paryushan Parva is about Amari Pravartan — taking a firm vow to abstain from violence (ahimsa) and to purify the mind and conduct. It marks the beginning of intensified self-discipline, prayers, and vows for the rest of the period, with emphasis on avoiding harm in thought, word, and deed. In Shwetambar practice this kick-off is central to setting the tone for the eight days; Digambar observances (Das Lakshan Parva) begin around the same spirit of ethical renewal, though there are sect-specific details.

Key ideas on Day 1:

• Begin self-purification, renew vows (vratas), and focus on ahimsa.
• Increase prayers, meditation, and study, while planning penance and forgiveness practices for the days ahead.
• Prepare to engage in Pratikraman, Kshama (forgiveness), and sraddha toward right conduct.

You can read more here and here .