You will get a vignette sticker when your visa application is approved. At Manchester Met we call this your travel visa. You have permission to come to the UK within 30 days of receiving your travel visa. The travel visa allows you to enter the UK and is not proof of your immigration permission.
Your actual immigration permission is in the form of a Biometric Residence Permit (BRP). You can collect your BRP after you arrive in the UK. Your BRP is the documentary evidence of your UK immigration permission. Check your decision letter as it will tell you which Post Office branch you can visit to collect your BRP. You must collect your BRP before the travel visa in your passport expires. Your decision letter outlines the conditions of your immigration leave, so it is essential that you keep it safe. You will need to take this letter, together with your passport and travel visa, when you collect your BRP at the Post Office branch. For more information about BRP, please visit the UKVI website here.