there are two ways of deploying a webpart  in your portal.
One you can do it manually and the next you can deploy it using a cab file.

first method.

create your webpart. copy your .dll into the C:\inetpub\wwwroot\bin directory.
then open the web.config file  under C:\inetpub\wwwroot
and add your webpart to the Safe controls list.
<SafeControls>
<SafeControl Assembly="CustomWebParts, Version=1.0.2.2, Culture=neutral,
PublicKeyToken=8af2443a8fe6763e" Namespace="CustomWebParts" TypeName="*"
Safe="True" />
</SafeControls>

save and close the file.

once you have done this go to WebPart gallery
each site  has its own webpart gallery

For the portal site you can find it under
SiteSettings>Manage security and additional settings> Manage web  Part gallery
for the WSS sites you can find it under
SiteSettings>Go to site administration> Manage Web part  gallery

from the webpart gallery select New Webpart and all webparts registered  as safe
are listed there, select your webpart and choose Populate Gallery.

That does it for you.

Second method.

Create a cab and deployment project to your webpart solution. Right click on
the cab project in the solution explorer and choose Add->Project output. Choose
Primary output and content files from the dialog and select OK.

compile the solution. The cab file will be created.

then using this command from the dos command prompt

stsadm -o addwppack -filename <path and filename of the cabfile> -globalinstall
-force

this deploys the webpart to the required directory and makes entries int he
web.config file.

once you have done this go to WebPart gallery
each site has its own webpart gallery

For the portal site you can find it under
SiteSettings>Manage security and additional settings> Manage Web Part gallery
for the WSS sites you can find it under
SiteSettings>Go to site administration> Manage Web Part gallery

from the webpart gallery select New Webpart and all webparts registered as safe
are listed there, select your webpart and choose Populate Gallery.