Hi Leif,
This is a big topic, but here is my attempt to answer it in a simple manner, from a user point of view (mine). I’m sure my interpretation has some holes in in and others may provide other definitions. This is a general overview.:
1)
- portals – small “p”, is being used all over the web-world now. “portal” (with a small “p”) in esri terms typically refers to ArcGIS Online (“AGOL” or “AGO”) and Portal for ArcGIS (“Portal”…notice the “P”). I know more about AGOL since I haven’t used Portal much, but the capabilities should be similar.
- AGOL – is, to use another buzz is “in-the-cloud”, that is not on your server.
- Portal – is installed in-house. The is typically if you want things to be kept totally within your network/firewall.
- Both require “named-users” to access administrative tacks and/or secure services (that a proxy or token isn’t provided)
- AGOL is provided with Desktop that is on maintenance…AGOL/Portal for the enterprise is included to some degree if you have ArcGIS Server on maintenance….but for any licensing or this and/or any of the other software, you would want to talk with a customer service rep or local distributor.
- Can “host” services
- Used to author maps using hosted services (by you and/or that are public), ArcGIS Server services, etc. Web Application Builder is one of these.
- Some analytical ability.
- Used as a “portal” (small “p”) for many of the other esri tools , including mobile, such as Collector, Web Appbuilder Developer Editiion, etc. These are man of these so Apps might be the best place to explore some of them.
- ArcGIS OpenData is included with a AGOL Enterprise version...and maybe other...which allows you a portal for allowing others to view and download you data. (I've just started working on this for our organization....too new to provide much more input)
- ArcGIS Server (also referred to as just “Server” or AGS)
- Installed in-house (or there are Amazon-cloud options, but I haven’t used any of those).
- License at different levels provides different capabilities
- What I use our for is to create services:
- to make it easier/faster for staff/public to access data….both dynamic and (pre-)cached
- can create custom geoprocessing (GP) services that can do specific, non-out-of-the-box tasks. This makes the possibilities semi-endless.
- GP services like finding a location can be provided thru AGS….or also are available thru AGOL
- feed into AGOL and the other web appications.
- Use our MSSQL to handle our advanced features on our master databases (i.e versioning, multi-user editing, topology, etc.)
- Javascript – including JS API and Web Appbuilder Developer Edition (WAB)
- Javascript is a scriptiong language popular with web development because most browsers can accept it (unlike Flash/Flex and Silverlight…which are now fading). It is typically used with some flavor of HTML.
- Javascript API – (application programming interface) are common. Esri has their own set of tools for arcgis. You can use this to create web pages “from scratch”, among other things, however there are so many samples, that you typically cut/paste/modify.
- The Web Appbuilder is available as a template in AGOL, and those can be downloaded and used with a compatible version of the Dev Edition….which can also author them on its own. Portal also has these capabilities, but lags behind a little. AGOL functionality is released first, followed by Dev Edition, then Portal.
- The WAB Developer Edition community is very active on GeoNet right now, so easy to find tools or help if needed.
- These can take services from AGOL/Portal/AGS.
- Python – just to throw another language out there….this is the scripting language for ArcGIS that helps in creating GP services, or doing other tasks. Fairly easy to use and learn. Strong Geonet user community. There are other programming languages that can get into all of this.
2) See if my explanation above helps. I will include some links below that might help with all of this, but would hurt to talk with a customer service rep too.
Links:
There are many more links that could be provided, but some of those will get you to the top-level overview.
Hope this helps.
edit: adding another link Documentation | ArcGIS for Server might want to look at the overviews for AGS and Portal
