Find the gene record that you want in the NCBI Gene database.  (If your search returns too many records, see these tips for searching for genes.) Then apply one of the following methods that will allow you to obtain the transcript/protein sequence for the gene:

Method 1:

• Select the Full Report display (example).
• Select the link to the NCBI Reference Sequences (RefSeq) from the Table of contents on the right side of the screen.  The link will take you to the section of the Gene record that reports RefSeqs for the gene. (To learn more about the NCBI RefSeq project, please see the project's home page and this factsheet.)
• Scroll to the section(s) labeled mRNA and Protein(s). There will be more than one mRNA/Protein record if there are known transcript splice variants/protein isoforms for the gene. 
• Select the record (for example NM_ for a transcript) by clicking directly on its accession number, for example NM_001081128.3, which will display the transcript (mRNA sequence) Nucleotide record.
• Change the display to FASTA format to obtain the sequence itself (example).
• The steps for accessing the RefSeq protein sequences are the same. Select the NP_ records, for example NP_001074597.1

Method 2:

• Change the record display from Full Report to Gene Table (the display menu is located on the left side above the record).
• If you are working with eukaryotic genes that have transcript variants, select the variant that you want and click the + to expand the Exon table.
• Each Exon table provides links to the transcript (NM_ or XM_) and protein (NP_ or XP_) records. Additionally, exon listings in the tables provide links to each individual exon sequence.

Note that NCBI RefSeq staff do not generate individual transcript sequences for prokaryotes.