A shop sends more offers than you want, but you still need its order messages. Before pressing Block, decide whether the problem is one mailing list or every future message from that address.
In Gmail, blocking a sender sends their future messages to Spam. It does not remove your address from their mailing list. Unsubscribing asks the sender to stop the relevant subscription; Gmail says this can take a few days. Neither action is the same as deleting the messages already in your mailbox.
For a newsletter you recognise
Open the message in Gmail on a computer. If an Unsubscribe option appears beside the sender’s name, use it and read the confirmation. Some senders direct you to their website. One message’s unsubscribe option may cover only one of that sender’s lists, so check which subscription you are leaving.
For example, stopping a weekly product roundup may leave a separate events newsletter active. If another email arrives, compare its sender and list before concluding that the first request failed. Allow for the stated processing delay.
For a sender you want to block
Open a message, use More beside Reply and choose the option to block that sender. Review blocked addresses under Settings → See all settings → Filters and Blocked Addresses if you need to reverse the choice.
For suspicious junk, use Gmail’s reporting controls instead of following an unfamiliar unsubscribe link in the message body. Before blocking a shop’s address, check whether useful receipts also come from it: those future messages may end up in Spam too.