In stratified method, the data is divided into different groups on the basis of their homogenity(similarity).
In quota method, investigator divids the data as per the propotion and select sample from every group. The data of every group could not be similar.
In purposive sampling, the investigator selct the sample as per its judgement. The investigator judges which item have to be selected for sampling.
In convience method, the investigator select the investigation as per easiness. Take an example as investigator had to collect data about students, then if a school is near to him/her, then she/he will go to its nearest school ,not to farther schools. this is convience sampling.