Hello I am trying to obtain a substantial understanding of the concept entailed in the following quotation. Do you have any one who can break this down to laymens terms and explain the data collection effort associated with Grounded Theory?

Grounded theory

Data collection and data analysis occur concurrently, taking an iterative process. Purposeful sampling is initially used but then sampling is based on theoretical relevance to the developing theory, a process known as theoretical sampling; this continues until there is theoretical saturation or sufficiency.