Is it hard ordering clothes and shoes online? [please help]?

i have 2 questions about ordering clothes and shoes online 1 what if you order them and the shirt shorts or shoes are 2 small? and how does the people that send them get the clothes or shoes in your mailbox? i just want to know before i order them online and i never ordered clothes and shoes before just cds and books!!!! and if they leave them at your doorstep how do u know someone wont take them?