To open several sequences use the File->Open menu item or Open toolbar button and using Ctrl select the several sequences and click the Open button. The following dialog will appear:
...
The following parameters are available:
Separate sequence mode - open opens the sequences as separate sequences.
Merge sequence mode - merges sequences into one sequence with selected number of unknown symbols between sequences,.
Join sequences into alignment - joins sequences into alignment.
...
Choose the parameters and click the Open button. Sequences will be opened in the selected mode.
...