Distance healing is a popular technique used by many healers.
How far it could reach depends very much on your creative imagination. The stronger your intention, the more powerful and effective it would be.
All crystals' healing properties can be sent remotely. However one of the more frequently used crystal to send healing remotely is Goldstone. Apart from the healing properties from the crystals, some healers may like to send with a combination of Reiki energy, Belvaspata modality, blessing from the respective guide or individuals
For a beginner, just calm your mind and imagine linking your heart to the heart of the individual/ place/ etc. After which set intention to send healing across... just trust .. no specific forms/ colors/ patterns & etc. Recite that all that resonates with the highest purpose of the individual be received accordingly