[TYPO3-english] How to install extensions?

[Rowan Sylvester-Bradley]

I am brand new to TYPO3, so this is certainly a beginner's question. I have
installed introductionpackage-4.7.0 on my web server (I copied the file
introductionpackage-4.7.0.tar.gz to my web server, extracted it and ran the
installer).

I now need to install an application supplied by someone else. This consists
of three extensions. He says that to install them I have to upload the
extension directories into typo3conf/ext, and use the "Install Extension"
function of Extension Manager to install them. I have uploaded them, and I
can see them in the list of extensions, but when I select Extension Manager
there is no Install Extension function visible. I see a drop-down menu at
the top, which contains only one item: Extension Manager. Then I see four
tabs, Available Extensions, Import Extensions, Language Packages and
Settings. None of these seems to contain an Install Extension. With the
Available Extensions tab selected I then see a Filter field, then the list
of extensions (including my new ones).

How do I install these extensions?

Thanks - Rowan