On the main GC site menubar, on the right side, there is the "Upload" button. It appears whether you are in the dashboard, activities, calendar, reports, goals, or health.
The bar on the top of the table on the activities summary page has a "(+) Manual Activity" button. To me, uploading and adding an activity manually are closely related. It seems odd that I can't add a manual activity from the dashboard, which apparently is the most important page as it is the default one you get routed to for my connect, but you can add on manually from the activities summary page.
One can also add an activity manually on the calendar page, using a completely different mechanism (click on the square gray [+] symbol and pick a submenu item, vs clicking on the red round (+) symbol on the activities page).
A goal can be added from either the calendar page with the previously mentioned square gray plus symbol, or by clicking the "+ Create a New Goal" tab (!) on the goals page.
On the health page, manually adding data is done by a different looking button from all the others.
They all have "+" in common, but graphically, they are all over the map.