How to import data from miseq paired end reads 2 x 251

Hi, thank you very much for your response. I now have a reads.fastq file and a barcode.fastq file. I have already imported the files to qiime2 using the EMPSingleEndSequences type. I tried to do demultiplexing sequences--for sample metadata.tsv, I used the mapping.txt that I have. It's written in the tutorial section to use *.tsv, but the *.txt that I've used did not give errors, so I supposed that it is okay? However, when I tried viewing demux.qzv using qiime2 gui so I can decide trim and trun length, I find my graph weird. I must have done something wrong here?

My apology if this question may appear stupid--new to qiime/bioinformatics.

Please let me know how to proceed and thank you for your patience.