You can go to the yahoo site yahoo.com and sign in, or you can setup your mail program to download the messages. You don't mention how you want to access your email. If you have a mail client, the settings are here:
pop settings:
POP access settings and instructions for Yahoo Mail
imap settings:
IMAP server settings for Yahoo Mail
imap is newer. If you use a modern mail client, like thunderbird, enter username and password, and the client will be auto configured for yahoo
Thunderbird is free and can be downloaded here:
Mozilla Firefox
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