First, MC uses the tag [Album Artist] to group tracks into an album. All tracks have to have the same [Album Artist] to be part of an album. MC creates [Album Artist] for you from the [Album] and [Artist] tags. So, once you have the artist and album tags set correctly, those tracks will show as an album.
If the file structure contains the artist and album name, the easiest way is to have J River use the information in the filename of the imported files to populate the tags. The most popular folder format is to have a folder with the artist name and a sub-folder with the album name and the tracks names as track number track name. That is [Artist]\[Album]\[Track #] [Name]. The idea is to tell MC what folder structure you have and then let it read the data and create the tags. To do that Select a track and highlight it (left mouse button) and then right click and select Library Tools - Fill Properties from Filename. The Automatic option should work. Otherwise you can set the specific options for the Directories and the Filename. Try that on one track and see if it fills in the album and artist correctly. If that works correctly, then try a few more and eventually do all of them. If you want to look at the filenames, look for it in one of the columns of the list. If it is not there, you can right click on the header (like Album) and choose Filename from the list. That will crate a column with the filename in it. You can also display [Album Artist[] this way. (I am assuming you are in what is called Standard View, which displays the album cover and the track list below that.)
If the album/artist information is not in the filenames, then you have to do the tagging manually. As long as the album name is there, it is pretty easy. In your list of tracks, sort it by album name by clicking on Album in the header and choose Sort Inside Group by Album. Then select all the tracks in an album using standard Windows conventions (Control Left Mouse to do individually or Shift Left Mouse to select a group). Right click on the highlighted tracks and choose Tag. In the tag window (lower left) enter the artist name. You can also look at Album Artist to be sure they all have the same value. Repeat for each album. Otherwise, if the album tag is blank but the artist tag is populated, you can so a similar process based on artist. If neither artist or album is there, you will need to either fill in the artist and album for each track, or you can select all the tracks from one album and tag them as a group. If you need to do this, you can sort the display by Filename and that should group the tracks from one album together if there is a common file structure based on album or artist.
Hopefully, you will be able to get the tags populated from the filenames. That is the easiest way.
As far as album art, once you have the tracks separated into albums, you can right click on an album and choose Cover Art - Get from Internet. That will search for the cover art and if it is not an obscure album it will find it for you. You can select multiple albums at one time and it will work through each one. If that does not find the cover art, there are other options, but I would start there.
Give it a try and ask for more help if needed.