uploading image asp.net Core

You should inject IHostingEnvironment so you can get the web root (wwwroot by default) location.

public class HomeController : Controller
{
    private readonly IHostingEnvironment hostingEnvironment;
    public HomeController(IHostingEnvironment environment)
    {
        hostingEnvironment = environment;
    }
    [HttpPost]
    public async Task<IActionResult> UploadFiles(List<IFormFile> files)
    {
        long size = files.Sum(f => f.Length);

        // full path to file in temp location
        var filePath = Path.GetTempFileName();

        foreach (var formFile in files)
        {
            var uploads = Path.Combine(hostingEnvironment.WebRootPath, "images");
            var fullPath = Path.Combine(uploads, GetUniqueFileName(formFile.FileName));
            formFile.CopyTo(new FileStream(fullPath, FileMode.Create));

        }
        return Ok(new { count = files.Count, size, filePath });
    }
    private string GetUniqueFileName(string fileName)
    {
        fileName = Path.GetFileName(fileName);
        return  Path.GetFileNameWithoutExtension(fileName)
                  + "_" 
                  + Guid.NewGuid().ToString().Substring(0, 4) 
                  + Path.GetExtension(fileName);
    }
}

This will save the files to the images directory in wwwroot.

Make sure that your form tag's action attribute is set to the UploadFiles action method of HomeController(/Home/UploadFiles)

<form method="post" enctype="multipart/form-data" asp-controller="Home"
                                                  asp-action="UploadFiles">
    <div class="form-group">
        <div class="col-md-10">
            <p>Upload one or more files using this form:</p>
            <input type="file" name="files" multiple />
        </div>
    </div>
    <div class="form-group">
        <div class="col-md-10">
            <input type="submit" value="Upload" />
        </div>
    </div>
</form>

I am not very certain why you want to return Ok result from this. You may probably return a redirect result to the listing page.

File upload in ASP.NET Core MVC in simple steps

1.Demo.cshtml View Code snippet

<form method="post" enctype="multipart/form-data" asp-controller="Demo" asp-action="Index">
<div class="form-group">
    <div class="col-md-10">
        <p>Upload one or more files using this form:</p>
        <input type="file" name="files" multiple />
    </div>
</div>
<div class="form-group">
    <div class="col-md-10">
        <input type="submit" value="Upload" />
    </div>
</div>

2. DemoController

For showing demo i have created a Demo Controller which has 2 Action Methods in it one to handle Get Request and another to handle post request.

using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using System;
using System.IO;
using System.Net.Http.Headers;

namespace WebApplication6.Controllers
{
    public class DemoController : Controller
    {
        private readonly IHostingEnvironment _environment;

        // Constructor
        public DemoController(IHostingEnvironment IHostingEnvironment)
        {
            _environment = IHostingEnvironment;
        }

        [HttpGet]
        public IActionResult Index()
        {
            return View();
        }

        [HttpPost]
        public IActionResult Index(string name)
        {
            var newFileName = string.Empty;

            if (HttpContext.Request.Form.Files != null)
            {
                var fileName = string.Empty;
                string PathDB = string.Empty;

                var files = HttpContext.Request.Form.Files;

                foreach (var file in files)
                {
                    if (file.Length > 0)
                    {
                        //Getting FileName
                        fileName = ContentDispositionHeaderValue.Parse(file.ContentDisposition).FileName.Trim('"');

                        //Assigning Unique Filename (Guid)
                        var myUniqueFileName = Convert.ToString(Guid.NewGuid());

                        //Getting file Extension
                        var FileExtension = Path.GetExtension(fileName);

                        // concating  FileName + FileExtension
                        newFileName = myUniqueFileName + FileExtension;

                        // Combines two strings into a path.
                        fileName = Path.Combine(_environment.WebRootPath, "demoImages") + $@"\{newFileName}";

                        // if you want to store path of folder in database
                        PathDB = "demoImages/" + newFileName;

                        using (FileStream fs = System.IO.File.Create(fileName))
                        {
                            file.CopyTo(fs);
                            fs.Flush();
                        }
                    }
                }


            }
            return View();
        }
    }
}

Snapshot while Debugging

Location of folder where Images are stored